The technical collaboration program of IEA Geothermal, has, since 1997, through its Working Group 1, undertaken cooperative research studies on environmental and social issues relevant to advancing development of new renewable geothermal resources and sustaining production from existing geothermal systems, by using state-of-the-art technology and best-practice procedures. The goals of the group are: 1) to encourage the sustainable development of geothermal energy resources in an economic and environmentally responsible manner; 2) to quantify and balance any adverse and beneficial impacts that geothermal energy development may have on the environment, and 3) to identify ways of avoiding, remedying or mitigating adverse effects. Tasks include: a) addressing impacts on natural features by monitoring surface thermal feature and ecosystem changes and devising techniques to avoid or mitigate adverse impacts, while encouraging beneficial effects; b) rectifying discharge and reinjection problems, including gas emissions (CO2 & H2S), chemical contamination of water, subsidence, scaling and corrosion, treatment options, and reinjection strategies; c) developing methods of impact mitigation and environmental procedures through an analysis of issues, procedures, efficient policies, protocols, effective compliance, and successful strategies to address social and environmental effects; d) sustaining utilisation by undertaking long-term reservoir simulations, optimizing future operational strategies, improving recharge factors and recovery times, improving reservoir performance, and applying holistic sustainability protocol indicators. This paper summarizes the recent outcomes of that collaboration amongst eight participating countries: Australia, Iceland, Italy, Japan, New Zealand, Norway, Switzerland and the United States. One highlight has been the raising of international awareness of successful mitigation schemes and beneficial environmental or social outcomes.

Volcanic-hosted epithermal Au-Ag quartz vein deposits in the Hauraki Goldfield are investigated using a range of geophysical methods. Tools such as airborne magnetics and ground-based resistivity have focussed on mapping alteration zones, lateral contacts in the volcanic rocks, and prospect scale faults. Reviewing the merits of each geophysical method is valuable as it provides exploration teams with the background material required to apply the most effective tools. The review compiles existing data and summarises the rock properties useful for constraining geophysical models. The Golden Cross mine in the Waitekauri Valley is used to illustrate the strengths and limitations of various techniques. Electrical resistivity is the most valuable rock property to target exploration, but magnetic surveying and gamma-ray spectrometry can reduce the ambiguity between quartz-rich mineralised zones and un-altered volcanic host formations. Density and porosity variations caused by alteration can be mapped with gravity data provided the regional field is defined.

Assessing changes in surface heat-loss at geothermally active areas provides insight into the geothermal reservoirs at depth. Surface temperatures and heat output of steam-heated ground can be inferred through processing of thermal infrared images, as well as by direct measurements using terrestrial calorimetry. In February 2014, a high resolution aerial thermal infrared (TIR) survey and a terrestrial heat-loss survey (excluding fumarole discharge) were carried out over Karapiti (ca. 0.35 Km(2) in the Wairakei-Tauhara Geothermal System) in the Taupo Volcanic Zone, New Zealand. Estimates of heat-loss are compared to those calculated from TIR data collected by the Landsat-8 satellite of the area. This paper discusses the processing techniques for the datasets and compares inferred surface heat losses. The aerial TIR and terrestrial measurements are in reasonable agreement with calculated surface heat-loss values for Karapiti range from 41 MW (theoretical radiation heat loss using aerial TIR) to 58 MW (total heat loss based on an empirical correlation with boiling-point depths). Satellite images show a large variation between day-time and night-time TIR assessments. The assessment of nocturnal (non-solar), radiation heat-loss is an order of magnitude lower than the total heat-loss determined from the other techniques and approximately 1/3 of the inferred radiated component calculated from the aerial TIR data. This is likely to be a consequence of diffuse, advecting-steam heat-loss, combined with an image resolution issue: the pixel resolution of the satellite image (30 x 30 m) is much larger than the typical size of the active geothermal surface manifestations (< 10 m(2)). Because the radiated heat-loss is a non-linear function of land surface temperature, the in-pixel averaging under-estimates the radiated heat-loss. These and other problems currently restrict the usefulness of repeat low-resolution satellite imagery for monitoring of surface heat loss changes in steam-heated ground.

Maciej Lukawski, Jefferson W. Tester, Betina Bendall, Barry Goldstein, Gerardo Hiriart, Luis Gutierrez-Negrin, Ruggero Bertani, Christopher Bromley, Ernst Huenges, Arni Ragnarsson, Mike Mongillo, John W. Lund, Ladislaus Rybach, Vladimir Zui and Hirofumi Muraoka Cornell Energy Institute, Cornell University, Ithaca, NY, USA Energy Resources Division, South Australian State Government, Adelaide, Australia Energias Alternas, Estudios y Proyectos, Cuemavaca, Mexico Mexican Geothermal Association, Morelia City, Mexico Enel Green Power North America, Pisa, Italy GNS Science, Wairakei Research Centre, Taupo, New Zealand GFZ-Potsdam, Potsdam, Germany Iceland GeoSurvey, Reykjavik, Iceland Geo-Heat Center, Oregon Institute of Technology, Klamath Falls, OR, USA Geowatt AG, Zürich, Switzerland Research-Production Centre for Geology, Minsk, Belarus Hirosaki University, Hirosaki, Japan

Geophysical monitoring tools such as micro-gravity, micro-seismicity and ground deformation provide geothermal reservoir modellers and resource managers with improved information on reservoir behaviour, especially when fields are under development. As-aconsequence, better production and reinjection strategies can be tested, and future operational scenarios can be fine-tuned to improve utilisation sustainability. Advanced and novel monitoring methods also help improve forecasts of near-surface environmental effects and monitor the results of mitigation efforts undertaken through adaptive reservoir management. This paper reviews current knowledge gained from such methods and discusses the potential for using this knowledge to help develop better strategies for resource expansion and make-up drilling strategy. Recent advances in research into continuous monitoring techniques using geophysical methods include the use of: micro-gravity, seismic-tomography, ground-deformation, repeat resistivity and various forms of remote-sensing. Knowledge has also been gained from reviewing the decades of monitoring of physical changes that have occurred in conventional geothermal projects around the world. To make full use of this information, and to accurately simulate geophysical property changes resulting from reservoir fluid and heat transport, advanced reservoir modelling benefits from coupled thermal, hydraulic, mechanical, and chemical (THMC) processes. Consequently, rock properties used in reservoir simulation, such as permeability and porosity, are variables rather than constants over the lifetime of a reservoir. The benefits of this improved understanding of reservoir processes is an improvement in conceptual models of geothermal resources and therefore better projections of their sustainable energy extraction capacity and recharge parameters. This knowledge is also applied to exploration and expansion strategies to provide better drilling targets and improved production-reinjection strategies for wellestablished, but aging, geothermal developments.

Collaborative research into sustainable and environmentally-sound development strategies is carried out under the auspices of the IEA Geothermal Implementing Agreement (IEA-Geothermal) (www.iea-gia.org), through the Tasks of its Annex 1, Environmental Impacts of Geothermal Development. Cooperation amongst member countries facilitates knowledge sharing and exchanges of geothermal operational and modeling experience. This is vital in order to learn from past successes and mistakes. By growing investor confidence in the long-term sustainable development of geothermal resources, and avoiding or mitigating adverse local environmental effects, we can materially advance global efforts to mitigate the much more serious adverse effects of climate change resulting from fossil-fuel carbon emissions. Analysis of long-term historical performance of developed geothermal reservoirs, together with simulations of their likely future performance using reservoir models, leads to important conclusions regarding optimizing sustainable strategies for future development. A key factor is the choice of initial and subsequent staged capacity installments; these are justified by increasingly more-sophisticated reservoir simulation models. The objective is to avoid excessive pressure or temperature draw-down, but to allow for sufficient reservoir response to provide good history matching. A second key factor is the ability to adapt reinjection strategies (location, depth, fluid chemistry and temperature) as new information from monitoring of production/injection effects becomes available. The third key factor is the early recognition of the dynamic response of a resource to its utilization, with good information collected on the source location, chemistry and temperature of induced recharge fluids. Improved tracer technology helps characterize parameters such as permeability, diffusion and fluid storage between injection and production sectors. Better calibration of reservoir models improves characterization of the permeability structure and boundary recharge parameters that dictate long-term reservoir behavior. Over very long timescales (>100 years) reservoirs are likely to trend toward a pseudo steadystate wherein induced mass and heat recharge almost balance the net mass and heat that can be extracted. Other options for sustainable development, however, might involve cyclic or intermittent energy extraction (‘heat grazing’) wherein parts of a large heat resource may be developed and recovered in rotation. Strategies must also take into account potentially adverse local environmental effects. An alternative long-term strategy is to use the acquired knowledge and simulated behavior from early production stages to plan deeper drilling, by targeting the primary up-flows. Over time, the shallow parts of a resource are ‘retired’ and bore-holes tap directly into higher enthalpy and more productive sectors of the resource. Challenges associated with this strategy include the need to reduce the cost of deep drilling, and to develop technologies to deal with super-critical and potentially corrosive reservoir fluids. However, the rewards could be significant.

Subsidence, and its effects, from conventional geothermal operations in New Zealand have been well documented and closely studied for many decades. Examples are presented here of local subsidence anomalies that show associations with relativelyshallow, anomalously-compressible, porous formations, weakened by hydrothermal alteration from boiling fluids that passed through shallow outflow structures. Pressure decline, originating from deep production, but diffusing slowly into shallow aquifers and aquicludes, has previously been attributed as the principal cause. Anomalous deformation is found to be the product of subsurface changes in effective stress (either pressure or temperature in origin), acting on a thick sequence of clays, or fractured rocks, which exhibit anomalous geo-mechanical properties. Consideration of the transition between brittle failure and ductile behaviour across a range of temperatures and rock types is also needed. Settlement can increase over time due to non-linear stressstrain relationships such as clay yielding. This paper reviews New Zealand geothermal case studies from Wairakei, Tauhara, Ohaaki and Kawerau, where applications were recently granted for resource consent renewal or development expansion. These efforts have stimulated additional studies of observed changes in subsidence rates, corresponding horizontal deformation, inferred deformation mechanisms, model predictions and possible mitigation options. Mechanisms involving subsurface temperature change and chemical alteration, as well as transient pressures, are sometimes implicated. Transient tectonic creep, ‘shake-induced’ subsidence and groundwater level fluctuations acting on buried deposits of unconsolidated alluvium, are also plausible mechanisms for fluctuating deformation rates of natural origin in some settings (for example, Kawerau). To properly simulate the deformation processes, fully inter-coupled Thermal-Hydraulic-Mechanical-Chemical modelling would be preferred, but history matching suffers from a plethora of variables and a shortage of good subsurface data. Fundamental rock properties used in traditional reservoir simulation, such as permeability, porosity and stress state, which are usually treated as constant parameters in history matching and subsequent scenario predictions, turn out to be significant variables in deformation modelling. Alternative and more pragmatic modelling approaches that simplify the geothermal subsidence process have proven to be reasonably successful where rate changes are smoothly varying, but predictions retain significant uncertainty, particularly where non-geothermal mechanisms are important, and where the hydro-geological properties of shallow layers are poorly represented in the simple models. However, adaptive mitigation options for adverse effects of subsidence, using comprehensive monitoring, are generally accepted. These are usually expressed in terms of targeted injection management to control pressure and temperature.

Summary Best practice procedures are being developed and implemented to deal with hazard mitigation of the effects of induced seismicity. Improved protocols and practical strategies are required to gain public acceptance. Developing such protocols is an important research objective ( Bromley & Majer, 2012 ). The strategies build on better understanding of the triggering mechanisms, and the underlying causes of induced seismicity. Some of the key questions that remain to be fully addressed are as follows: What methods can be used to differentiate between triggered, induced and natural seismicity? How can we improve estimations of the damaging potential of triggered earthquakes? How can we mitigate the seismic hazard due to resource exploitation? How should a monitoring network be optimally designed to deliver the required information for seismic hazard mitigation? How can an exploitation strategy be optimally designed to avoid causing large earthquakes? What decisions are influenced by the micro-seismic monitoring and interpretation results? [For example: stimulation optimization, reservoir production/injection management, or make-up drilling targets.] What are the best ways to build public acceptance for resource utilisation? Based on experience gained from many decades of geothermal exploration and development, often within earthquake-prone geological settings, these major questions regarding induced seismicity are discussed from the end-user point-of-view. Those issues which require more research are identified. Suggestions are offered to facilitate better cooperation between academic institutions and industry partners to foster information exchange and better serve public and company interests.

In February 2010 Contact Energy Limited lodged a comprehensive resource consent application with New Zealand's Environmental Protection Authority (EPA) for the 250MW Tauhara II Geothermal Power Station Development east of Taupo Township. It was the first development application to be processed by the EPA through a new fast track consenting process designed for projects of National Significance. This was a challenging project which involves developing New Zealand’s largest geothermal energy project on the door-step of Taupo Township. It required a range of complex technical and urban interface issues to be considered, particularly associated with historical and potential additional subsidence, noise, landscape, shallow-geothermal and air quality effects. There are also a wide range of Maori landowning and cultural interests in the project area. A number of innovative techniques were employed in the delivery of this project including facilitation of a Technical Focus Group (TFG) involving local Councils, the Department of Conservation and Maori members to guide and assess the draft consent documentation, and the development of a Steamfield Design Protocol to govern the on-going development of the steamfield works over time. Detailed conditions were also developed to allow an adaptive management approach to avoiding or mitigating any observed development impacts on important shallow geothermal resources (hot springs, fumaroles, thermotolerant vegetation, shallow heat users etc.). A Working Party approach successfully considered and agreed an offset approach for effects associated with Maori interests. Resource consents were granted for the project in December 2010 and subsequently the innovative and inclusive consenting process won major project awards from the New Zealand Planning Institute, New Zealand Resource Management Law Association and the New Zealand Institute of Landscape Architects.

New Zealand’s geothermal systems are mostly located in high-temperature, volcano-tectonic settings, but background levels of local natural microseismicity (micro-earthquakes) are quite variable. Triggered or induced seismicity effects from geothermal operations have also been very mixed. Understanding the reasons for these differences leads to better comprehension of the potential seismic risks and rewards (or opportunities) of different development options. Large-scale NZ geothermal projects started in the late 1950’s, but reinjection, the most commonly attributed cause of induced seismicity, only commenced in the mid 1980’s (at Wairakei). Here, initial injection trials were relatively shallow (~1.3 km) and triggered some local low-magnitude microseismicity, at high effective stimulation pressure (~5 MPa). Other, low-pressure, reinjection projects soon followed, with subsequent changes in injection strategy (depth, location, in-situ temperature, pressure and flow-rate). They included: Ohaaki (1988, deep to shallow), Kawerau (1992, shallow to deep), Rotokawa (1997, shallow to deep), Ngawha (1998, deep), Mokai (2000, shallow to deep), and Ngatamariki (2013, deep). A wide range of induced seismicity responses has accompanied these injection strategies and this paper provides an overview of these experiences. The overall objective of much of this research is to illuminate probable mechanisms, identify zones of potential fracture permeability enhancement from microseismic locations, thereby provide information on probable reservoir boundary conditions for simulation models, and help provide possible mitigation options, if (and when) induced seismicity magnitudes and felt event rates exceed acceptable values. At Ohaaki and Ngawha, natural seismicity rates are relatively low, and local induced seismicity (M>2) has not been detected, despite Ngawha’s 100% peripheral injection to ~1 km depth and Ohaaki’s 70% peripheral injection (<1km depth). At Kawerau, natural rates of seismicity are high (average 2 felt events/month), but there have been no obvious triggered events associated with production or injection changes, including an expansion and transition in 2008 from shallow (0.4 km) infield to mostly deep (2 km) peripheral injection. At Wairakei, Rotokawa, Ngatamariki and Mokai (adjacent systems), natural seismicity is moderate, but locally variable. Deep reinjection (increasing since 2006) has, in places, triggered moderate levels of microseismicity within inferred fault zones between injection and production sectors. The maximum magnitude recorded has been ML 3.5 (local network magnitude 3.1), but most are well below ML 2.5, and felt seismicity effects have not been an issue with the local rural inhabitants, who are familiar with similar-sized natural events. There is some evidence of cooling contraction increasing permeability with time, and microseismicity constrained by fault-controlled flow barriers. Our conclusion is that, in New Zealand, where examples of induced seismicity have occurred, the favoured mechanism is associated with the indirect effects of increased fluid-flow on pre-stressed, pre-existing, fracture networks. This flow induces stresses from cooling contraction, and is driven by pressure gradients through the fracture network, but triggers seismic failure only on favourably-oriented fractures, through thermal, chemical, or pressure transients, or by associated micro-stress perturbations, locally unlocking asperities on pre-stressed fractures. We propose several conditions that increase the likelihood that an operating geothermal field will experience reinjection-driven induced seismicity.

The patterns of triggered seismicity and subsidence effects from conventional geothermal operations are often irregular in their timing and location, and therefore difficult to predict, particularly in the absence of detailed knowledge of the local subsurface stress conditions, rock properties and permeability structure. Reinjection is usually identified as the principal cause of triggered seismicity, and ground subsidence effects are usually attributed to pressure decline from production. The real situation is more complex, however, and the two processes of subsidence and seismicity can be closely entwined. Both processes are products of subsurface stress changes acting on clays, rocks or fault surfaces, usually exhibiting anomalous geo-mechanical properties. Adaptive mitigation for adverse effects from either process calls for a coordinated approach, using injection management to control induced stress and strain changes, while considering the potential adverse effects of both deformation processes. This paper reviews several geothermal cases, and shows that interlinked mechanisms, involving temperature and chemical changes, as well as transient pressures, are implicated. Interlinked mechanisms such as ‘slow-deformation’ events or earthquakes, and ‘seismicity-induced’ subsidence, are probably more common in geothermal settings than we previously thought. Examples from New Zealand of triggered seismicity favor a mechanism associated with the indirect effects of increased fluid flow. The flow is driven by pressure gradients through a fracture network, but seismic failure is triggered only on pre-existing, favorablyoriented fracture-networks, and can occur throughout the fracture network affected by moving fluid. The triggering mechanism can be local temperature, pressure or chemical transients, or local stress perturbations, unlocking asperities on stressed fractures. Some subsidence and seismicity mechanisms require consideration of the transition between brittle and ductile behavior across a range of temperatures, pressures and rock types. Settlement can also originate from shaking of seismic origin and non-linear stressstrain relationships such as yielding. To simulate such interactions and deformation processes, what is required is a better conceptual understanding of deformation processes, and truly inter-coupled Thermal-Hydraulic-Mechanical-Chemical (THMC) modeling. Some of the more fundamental rock properties used in traditional reservoir simulation, such as permeability, porosity and stress state, which are usually treated as constant parameters in history matching and subsequent scenario predictions, are, in reality, time-variables, and this needs to be incorporated into the inter-coupled modeling.

Seismicity produced by human activities (i.e. induced seismicity) has been widely reported over the last 40 years. To date few induced earthquakes have been recorded at CO2 storage sites, however, the volumes of injected CO2 and the number of operational sites are small. A review of induced seismicity from different types of fluid injection and extraction sites confirms that these events are typically ≤4.5 in magnitude (M) and in many cases have no reported earthquakes. Although the size (and associated risks) of induced earthquakes at CO2 storage sites is most likely to be small, these events could decrease seal integrity or raise public concerns, while rare larger events (>M5) could also have ramifications for CCS beyond a single site. These risks can be reduced by careful site selection and development of site-specific risk reduction and mitigation programmes. Forecasts of induced seismicity using physical and statistical models and real-time monitoring will be key planning and decision making tools. The utility of monitoring and mitigation programmes will be maximized by establishing prior to injection, site performance and management guidelines for acceptable levels of induced seismicity, and agreed control measures. Further improvements to risk management practices, understanding induced seismicity processes and stakeholder confidence may be achieved by; a) increasing the number of publically available induced earthquake catalogues for development and testing of physical and statistical models, b) undertaking more systematic studies of individual sites populated by well constrained sub-surface geomechanical information and seismicity data complete down to small magnitudes (e.g., M-3), c) enhancing the physical reality of numerical dynamic models, d) studying the scaling effects of seismicity associated with moving from pilot projects to full commercial implementation of CO2 storage, e) developing standard risk management procedures and guidelines for induced seismicity at CCS sites and,f) filling induced seismicity knowledge gaps in the CCS community by collaborating with seismologists and modellers working in other industries.

Geothermal fluid has been extracted from the Wairakei field in New Zealand since the mid-1950s for electricity generation. This has induced regional subsidence of more than 1 m; in addition, there are a few localised bowls with much greater subsidence. A comprehensive geotechnical investigation with recovery of undisturbed samples from depths of up to 774 m was undertaken with testing of samples from within and outside subsidence bowls to determine material properties, with the aim of improved understanding of subsidence within the Wairakei–Tauhara geothermal system. Results from more than 130 K0 triaxial compression tests on core samples are discussed. Given the volcanic origins of most of the material present, a wide variation in the measured constrained modulus values is not surprising. Scanning electron microscope images reveal differences between the texture of the soft materials and the very stiff materials; these correlate with the constrained modulus values. The applicability of the Terzaghi effective stress equation is considered in relation to the measured property values; the conventional equation remains valid even for the least compressible materials tested.

Geothermal, as a source of renewable energy (power and heating), has the potential to meet 3–5% of global demand by 2050. For some high-temperature reservoirs, a technical challenge that may constrain deployment is ground subsidence caused by reservoir pressure decline. At the Wairakei–Tauhara geothermal system in New Zealand, an integrated geotechnical-geoscientific investigation of the causes of local subsidence anomalies (up to 15 m, accumulated over 50 years) has successfully identified and modelled the factors, mechanisms and processes involved. Zones of hydrothermally altered porous sediments and clays, at up to 400 m depth, display inelastic deformation behaviour, yielding to a highly compressible state once subjected to a fluid pressure decline. Monitoring shows that pressure dissipates slowly through these low-permeability capping formations. Adaptive management involves continued monitoring of subsidence rates, and sampling, analysis and predictive modelling where necessary. Simulation modelling indicates that long-term mitigation can be achieved by sustaining pressures through targeted shallow injection.

Shallow warm water resources associated with low enthalpy geothermal systems are often difficult to explore using geophysical techniques, mainly because the warm water creates an insufficient physical change from the host rocks to be easily detectable. In addition, often the system also has a limited or narrow size. However, appropriate use of geophysical techniques can still help the exploration and further investigation of low enthalpy geothermal resources. We present case studies on the use of geophysical techniques for shallow warm water explorations over a variety of settings in New Zealand (mostly in the North Island) with variable degrees of success.A simple and direct method for the exploration of warm water systems is shallow temperature measurements. In some New Zealand examples, measurements of near surface temperatures helped to trace the extent of deeper thermal water.The gravity method was utilised as a structural technique for the exploration of some warm water systems in New Zealand. Our case studies show the technique can be useful in identifying basement depths and tracing fault systems associated with the occurrence of hot springs.Direct current (DC) ground resistivity measurements using a variety of electrode arrays have been the most common method for the exploration of low enthalpy geothermal resources in New Zealand. The technique can be used to detect the extent of shallow warm waters that are more electrically conductive than the surrounding cold groundwater. Ground resistivity investigations using the electromagnetic (EM) techniques of audio magnetotellurics(AMT or shallow MT), controlled source audio magnetotellurics (CSAMT) and transient electromagnetic (TEM) methods have also been used. Highly conductive clays of thermal or sedimentary origin often limit the penetration depth of the resistivity techniques and can create some interpretation difficulties. Interpretation of resistivity anomalies needs to be treated in a site specific manner.

The Unzen geothermal field, our study area is active fumaroles, situated in Shimabara Peninsula of Kyushu Island in Japan. Our prime objectives were (1) to estimate radiative heat flux (RHF), (2) to calculate approximately heat discharge rate (HDR) using the relationship of radiative heat flux with the total heat loss derived from two geothermal field studies and (3) finally, to monitor RHF as well as HDR in our study area using seven sets of Landsat 7 ETM+ images from 2000 to 2009. We used the NDVI (Normalized differential vegetation index) method for spectral emissivity estimation, the mono-window algorithm for land surface temperature (LST) and the Stefan-Boltzmann equation analyzing those satellite TIR images for RHF. We obtained a desired strong correlation of LST above ambient with RHF using random samples. We estimated that the maximum RHF was about 251 W/m2 in 2005 and minimum was about 27 W/m2 in 2001. The highest total RHF was about 39.1 MW in 2005 and lowest was about 12 MW in 2001 in our study region. We discovered that the estimated RHF was about 15.7 % of HDR from our studies. We applied this percentage to estimate heat discharge rate in Unzen geothermal area. The monitoring results showed a single fold trend of HDR from 2000 to 2009 with highest about 252 MW in 2005 and lowest about 78 MW in 2001. In conclusion, TIR remote sensing is thought as the best option for monitoring heat losses from fumaroles with high efficiency and low cost.

LANDSAT thermal infrared data (30 m pixel resolution), supported by spot ground measurements, were used in this study to investigate changes between 1990 and 2011 in the radiative heat flux (RHF) from the 0.5 km 2 Karapiti fumarole area, at Wairakei Geothermal Field, Taupo, New Zealand. An objective was to calculate the net RHF of the geothermal area in order to reduce the effect of solar heating in these satellite infrared images. The result showed that the RHF decreased between1990 and 2011 by a total of about 29 MW. The net RHF (geothermal radiative heat flux) decreased by about 13 MW from 2000 to 2011. Another method of estimating net RHF, by subtracting the total incident direct solar heat load, also showed a decreasing trend, from about 96 to 67 MW during the study period. A vegetation index from the LANDSAT-TM/ETM+ VNIR bands (NDVI) was used to undertake a landcover study. Results implied that the area of healthy vegetation at Karapiti progressively increased during this period. This supports the evidence for a decrease in geothermal heat losses, because the health of thermally-stressed vegetation is inversely related to shallow ground temperature. Images of apparent land-surface temperature (LST) were statistically sampled using a random spatial distribution of 100 points. Though the results show large variations with time, overall, there is a decreasing trend. As expected, there is a strong correlation between LST and RHF from all analyzed images. Spot ground estimations of heat flux using a calorimeter, when repeated, also showed, on average, a decreasing trend of heat flux between 2000 to 2009, although several sites showed stable heat flux. Further supporting evidence came from repeated ground-based temperature-depth profiles, which showed that the near-surface boiling point depth lowered in level at most sites between 2000 and 2011, although several sites located in actively-steaming bare-ground (~98°C at ~0.1m depth) remained relatively stable. In conclusion, satellite imagery and supporting groundbased evidence suggest a pattern of gradual decline (despite some time and spatial variation) in overall heat flux over the past decade from the Karapiti fumarole area.