Abstract To extract meter-length, large-diameter cores from live massive corals on shallow reefs we developed a versatile underwater pneumatic drill driven by a portable gasoline-powered air compressor carried onboard a small boat. This drill was used to obtain intact cores 8.0 cm in diameter and 0.5‐1.5 m long from Guam's coastal waters. Advantages of this pneumatic drill over standard hydraulic drills include (1) lower cost; (2) easier portability; (3) more stable, safer, and faster drilling; and (4) elimination of the need to carry and use hydraulic fluid on the coral reef. The pivotal innovation in the application of pneumatic technology was use of an air motor rather than a conventional handheld pneumatic drill. Another significant innovation was employment of a pneumatic water pump to provide a continuous flow that purges debris from the borehole and the cutting edge of the diamond drill bit. This drill can provide paleo-climate researchers and others interested in retrieving high-quality coral core samples with a reliable, economical, easy to operate, safe, and environmentally friendly alternative to more expensive and cumbersome hydraulic drills.

Karst vadose zone heterogeneity creates complex transmission and storage dynamics that affect the timing and magnitude of aquifer recharge. Young, high‐matrix permeability eogenetic karst aquifers may have significantly higher matrix storage than older, lower matrix permeability counterparts. In vulnerable and water‐limited karst regions, the timescales of storage may be important for seasonal and sub‐seasonal water resource management. We create a framework to quantify storage dynamics in karst aquifers using high‐resolution precipitation and groundwater levels from the Northern Guam Lens Aquifer in the US territory of Guam. We estimate recharge using the Water Table Fluctuation method, and then develop transfer functions between precipitation and recharge to quantify storage and release of water from the vadose zone. The transfer functions are partitioned into different flow pathways including conduit, conduit/matrix, and slowly draining matrix. Probability distributions are fit to each pathway to determine the average travel times of infiltrated waters. The results show that aquifer recharge through secondary porosity features typically occurs within a few hours of a rainfall event, but this rapid recharge accounts for only 12%–28% of total recharge. The majority of aquifer recharge (>70%) occurs within a month of a contributing storm event. An additional 10% of recharge, on average, took longer than a month to reach the water table. The framework established can help improve the hydrological modeling and freshwater management for karst aquifers.

Tropical cyclones are common to islands in western Pacific including Guam, and they bring large amounts of rainfall within a short duration, thereby triggering landslides. It is well understood that accurate modeling of the response of the hillslope to shallow landslides resulting from heavy rainfall in mountainous basins requires consideration of unsaturated soil mechanics principles. In this study, soil was collected from shallow depths along slopes of a reservoir in southern Guam, and soil water retention curves (SWRC) were obtained in the laboratory. Furthermore, results are presented from transient seepage analyses coupled with limit equilibrium method-based slope stability analyses on a typical slope. Comparison of results with and without a rainfall event captures the sudden drop in matric suction and factor of safety of the slope due to infiltration, which confirms that storm events are the leading cause of landslides in hillslopes located in tropical environmental settings.

The U.S. Drought Monitor (USDM) has been the de facto operational drought monitoring product for the United States for the last two decades. For most of this time, its coverage included the 50 States and Puerto Rico. In 2019, coverage was expanded to include the U.S.-Affiliated Pacific Islands (USAPI). The geography, geomorphology, and climatology of the USAPI significantly differ from those of the mainland U.S. (CONUS) and they posed a unique challenge for the USDM authors. Following National Oceanic and Atmospheric Administration (NOAA) priorities for development of products in collaboration with users in what is termed "use-inspired science", NOAA agencies conducted several workshops to identify data and impacts relevant for, and develop drought monitoring criteria appropriate for, the USAPI. Once the criteria were identified and data processing systems were set up, the USAPI were included as part of the operational USDM drought monitoring beginning in March 2019. The drought monitoring criteria consist of weekly and monthly minimum precipitation thresholds for triggering drought, and they follow the USDM "convergence of evidence" methodology for determining the severity level (Dx) of the drought spell.

Located on the northern edge of the West Pacific Warm Pool and having a developed economy and modern infrastructure, Guam is well positioned and equipped for obtaining natural records of the west Pacific maritime paleoclimate. This study was a proof of concept to explore whether useful climate proxy records might be obtained from coral at readily accessible, even if geochemically nonoptimal, coastal sites. A 50-year Sr/Ca record (1960-2010) was thus obtained from a shallow-water, near-shore Porites lutea colony at a recreational facility inside Guam's Apra Harbor and compared with local and regional meteorological records, including the El Nino-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) indices. The accessibility of the site enabled documentation of relevant environmental variables for 16 months (September 2009-December 2010): seawater delta O-18, pH, seawater cations, and nitrate. Time series of seawater delta O-18, pH, and cations show evidence of freshwater input from direct rainfall and stream discharge into the harbor. An anomalously higher mean and variable concentrations of Ba suggest the presence of river-borne, fine-grained terrigenous sediment. Nevertheless, the Sr/Ca time series reproduces a long-term warming trend seen in historical records of local air temperature and regional sea-surface temperature (SST) and closely tracks the ENSO and PDO indices over the entire 50-year record. The consistency of the results with Guam's historical instrumental records, previous coral delta O-18 results from Guam obtained by others, and previous Sr/Ca proxy results for SST in similar environments elsewhere demonstrate that accessible near-shore sites-where environmental conditions can be monitored-can produce useful Sr/Ca records of local and regional climate phenomena.

Assessing the sensitivity of groundwater systems to hydroclimate variability is critical to sustainable management of the water resources of Guam, US territory. We assess spatial and temporal variability of isotopic and geochemical compositions of vadose and phreatic groundwater sampled from cave drip sites and production wells, respectively, to better understand the vulnerability of the freshwater lens on Guam to variability in hydroclimate. We independently evaluate the existing conceptual model of the Northern Guam Lens Aquifer that is largely based on physical, as opposed to geochemical, observations. Sampling was conducted from 2008 to 2015, over which rainfall gradually increased. Major ion geochemistry and Sr isotope values of groundwater show varying influence from soil, limestone bedrock, and seawater. Geochemical modeling that can explain spatial variability in groundwater Na+ and Mg2+ concentrations and Sr/Ca and Sr-87/Sr-86 values indicates that groundwater compositions are dominantly controlled by mixing of freshwater with seawater and water-rock interaction. Differences between amount-weighted annual average precipitation delta O-18 values and groundwater delta O-18 values indicate a recharge bias toward the wet season, consistent with other tropical carbonate island aquifer settings. Infra- and inter-annual variations in Na+ concentrations and delta O-18 values in groundwater reflect sensitivity of recharge to seasonal variations in rainfall amount and changes in annual rainfall amounts. Our results indicate the influence of multiple modes of recharge on groundwater compositions and spatial variability in the sensitivity of groundwater to seawater mixing. This sensitivity of the freshwater lens points to the vulnerability of groundwater resources to changes in recharge associated with climate, land-use change, and increases in population.

Editor’s note: For easy download the posted pdf of the State of the Climate for 2018 is a low-resolution file. A high-resolution copy of the report is available by clicking here . Please be patient as it may take a few minutes for the high-resolution file to download.

Carbon dioxide concentrations in caves are a primary driver of rates of carbonate dissolution and precipitation, exerting strong control on speleothem growth rate and geochemistry. Long‐term cave monitoring studies in midlatitude caves have observed seasonal variability in cave p CO 2, whereby airflow is driven by temperature contrasts between the surface and subsurface. In tropical settings, where diurnal temperature cycles are larger than seasonal temperature cycles, it has been proposed that caves will ventilate on daily time scales, preventing cave p CO 2 from increasing substantially above atmospheric p CO 2 . By contrast, the relatively small temperature difference between the surface and subsurface may be insufficient to drive complete ventilation of tropical caves. Here we present results of an 8 year cave monitoring study, including observations of cave p CO 2 and carbonate chemistry, at Jinapsan Cave, Guam (13.4°N, 144.5°E). We find that cave p CO 2 in Jinapsan Cave is both relatively high and strongly seasonal, with cave p CO 2 ranging from 500 to 5000 ppm. The seasonality of cave p CO 2 cannot be explained by temperature contrasts, instead we find evidence that seasonal trade winds drive cave ventilation and modulate cave p CO 2 . Calcite deposition rates at seven drip sites in Jinapsan Cave are shown to be seasonally variable, demonstrating that speleothem growth rates in Jinapsan Cave are strongly affected by seasonal variations in cave p CO 2 . These results highlight the importance that advection can have on cave ventilation processes and carbonate chemistry. Seasonality in carbonate chemistry and calcite deposition in this cave affect the interpretation of speleothem‐based paleoclimate records.

In 2016, the dominant greenhouse gases released into Earth's atmosphere-carbon dioxide, methane, and nitrous oxide-continued to increase and reach new record highs. The 3.5 +/- 0.1 ppm rise in global annual mean carbon dioxide from 2015 to 2016 was the largest annual increase observed in the 58-year measurement record. The annual global average carbon dioxide concentration at Earth's surface surpassed 400 ppm (402.9 +/- 0.1 ppm) for the first time in the modern atmospheric measurement record and in ice core records dating back as far as 800000 years.One of the strongest El Nino events since at least 1950 dissipated in spring, and a weak La Nina evolved later in the year. Owing at least in part to the combination of El Nino conditions early in the year and a long-term upward trend, Earth's surface observed record warmth for a third consecutive year, albeit by a much slimmer margin than by which that record was set in 2015. Above Earth's surface, the annual lower troposphere temperature was record high according to all datasets analyzed, while the lower stratospheric temperature was record low according to most of the in situ and satellite datasets.Several countries, including Mexico and India, reported record high annual temperatures while many others observed near-record highs. A week-long heat wave at the end of April over the northern and eastern Indian peninsula, with temperatures surpassing 44 degrees C, contributed to a water crisis for 330 million people and to 300 fatalities.In the Arctic the 2016 land surface temperature was 2.0 degrees C above the 1981-2010 average, breaking the previous record of 2007, 2011, and 2015 by 0.8 degrees C, representing a 3.5 degrees C increase since the record began in 1900. The increasing temperatures have led to decreasing Arctic sea ice extent and thickness. On 24 March, the sea ice extent at the end of the growth season saw its lowest maximum in the 37-year satellite record, tying with 2015 at 7.2% below the 1981-2010 average. The September 2016 Arctic sea ice minimum extent tied with 2007 for the second lowest value on record, 33% lower than the 1981-2010 average. Arctic sea ice cover remains relatively young and thin, making it vulnerable to continued extensive melt. The mass of the Greenland Ice Sheet, which has the capacity to contribute similar to 7 m to sea level rise, reached a record low value. The onset of its surface melt was the second earliest, after 2012, in the 37-year satellite record.Sea surface temperature was record high at the global scale, surpassing the previous record of 2015 by about 0.01 degrees C. The global sea surface temperature trend for the 21st century-to-date of +0.162 degrees C decade(-1) is much higher than the longer term 1950-2016 trend of +0.100 degrees C decade(-1). Global annual mean sea level also reached a new record high, marking the sixth consecutive year of increase. Global annual ocean heat content saw a slight drop compared to the record high in 2015.Alpine glacier retreat continued around the globe, and preliminary data indicate that 2016 is the 37th consecutive year of negative annual mass balance. Across the Northern Hemisphere, snow cover for each month from February to June was among its four least extensive in the 47-year satellite record. Continuing a pattern below the surface, record high temperatures at 20-m depth were measured at all permafrost observatories on the North Slope of Alaska and at the Canadian observatory on northernmost Ellesmere Island.In the Antarctic, record low monthly surface pressures were broken at many stations, with the southern annular mode setting record high index values in March and June. Monthly high surface pressure records for August and November were set at several stations. During this period, record low daily and monthly sea ice extents were observed, with the November mean sea ice extent more than 5 standard deviations below the 1981-2010 average. These record low sea ice values contrast sharply with the record high values observed during 2012-14. Over the region, springtime Antarctic stratospheric ozone depletion was less severe relative to the 1991-2006 average, but ozone levels were still low compared to pre-1990 levels.Closer to the equator, 93 named tropical storms were observed during 2016, above the 1981-2010 average of 82, but fewer than the 101 storms recorded in 2015. Three basins-the North Atlantic, and eastern and western North Pacific-experienced above-normal activity in 2016. The Australian basin recorded its least active season since the beginning of the satellite era in 1970. Overall, four tropical cyclones reached the Saffir-Simpson category 5 intensity level.The strong El Nino at the beginning of the year that transitioned to a weak La Nina contributed to enhanced precipitation variability around the world. Wet conditions were observed throughout the year across southern South America, causing repeated heavy flooding in Argentina, Paraguay, and Uruguay. Wetter-than-usual conditions were also observed for eastern Europe and central Asia, alleviating the drought conditions of 2014 and 2015 in southern Russia. In the United States, California had its first wetter-than-average year since 2012, after being plagued by drought for several years. Even so, the area covered by drought in 2016 at the global scale was among the largest in the post-1950 record. For each month, at least 12% of land surfaces experienced severe drought conditions or worse, the longest such stretch in the record. In northeastern Brazil, drought conditions were observed for the fifth consecutive year, making this the longest drought on record in the region. Dry conditions were also observed in western Bolivia and Peru; it was Bolivia's worst drought in the past 25 years. In May, with abnormally warm and dry conditions already prevailing over western Canada for about a year, the human-induced Fort McMurray wildfire burned nearly 590000 hectares and became the costliest disaster in Canadian history, with $3 billion (U.S. dollars) in insured losses.

Since 12 October 1979, Typhoon Tip has officially remained the tropical cyclone associated with the lowest atmospheric pressure measured at sea level: 870hPa. The average winds over 1min were estimated at 165kn. On 7 November 2013, Typhoon Haiyan was the first cyclone to have been estimated at 170kn from satellite imagery. In the absence of aircraft reconnaissance, the minimum pressure has been estimated at 895hPa using the wind–pressure relationship. Using data observed at Guiuan meteorological station in the Philippines, we have estimated the minimum surface pressure in the eye of Haiyan. On the basis of the last pressure measurement of 910hPa at Guiuan, which was located at the outer edge of the eyewall, we estimated the pressure gradient for the 11km of the eyewall. This estimation was made using a comparison with the pressure gradient of the eyewall of two of the most intense tropical cyclones for which the pressures were precisely measured by aerial reconnaissance. During these airborne missions, Hurricane Patricia (23 October 2015), which formed in the eastern North Pacific, had a pressure of 879hPa, and Typhoon Megi (17 October 2010), which formed in the western North Pacific, had a pressure of 890hPa. At the time of the aircraft reconnaissance, the sustained winds of 180kn for Patricia (6h before the maximum wind of 185kn) and 160kn for Megi were comparable to the 170kn of Haiyan. Based on the pressure gradient calculated inside the eyewall of Patricia and Megi, we distinguished three scenarios for Haiyan. Each of them gives a minimum pressure at sea level below the 870hPa of Typhoon Tip, which was the world record holder.

Editor’s note: For easy download the posted pdf of the State of the Climate for 2016 is a very low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.

Editors note: For easy download the posted pdf of the State of the Climate for 2014 is a very low-resolution file. A high-resolution copy of the report is available by clicking here. Please be patient as it may take a few minutes for the high-resolution file to download.

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ABSTRACT The relevant literature on extreme rainfall events in the Pacific remains relatively sparse compared to other regions (e.g. the coterminous United States, Europe, etc.). Moreover, several recent reports on climate in the Pacific mention the paucity of extremes information and often list ‘trends in historical climate’ as a necessary next step. This scientific assessment meets this need by examining historical trends in and drivers of extreme rainfall events across the entire Pacific Basin, inclusive from Alaska southward to Australia, and longitudinally from the Philippines eastward to North America, with an emphasis on island and coastal locations (within 200 km of the coastline). There is evidence of a general decrease in the frequency of annual extreme rainfall events, yet the amount of extreme precipitation contributing to annual and seasonal totals appears to be on the rise. Region‐wide, the number of consecutive dry days is increasing for those locations that are already dry, while the number of consecutive wet days is increasing for the already wet locales. The data for extreme rainfall statistics are considered to be relatively high quality for trend detection, while the level of understanding of the physical causes behind extreme rainfall is positively high. Since the ability to analyze the changes in historical rainfall extremes with some confidence is relatively recent, understanding is expected to improve in the future with the advancement of new datasets and ‘climate reanalysis’ projects.

In 2013, the vast majority of the monitored climate variables reported here maintained trends established in recent decades. ENSO was in a neutral state during the entire year, remaining mostly on the cool side of neutral with modest impacts on regional weather patterns' around the world. This follows several years dominated by the effects of either La Nina. or El Nino events.According to several independent analyses, 2013 was again among the 10 warmest years on record at the global scale, both at the Earth's surface and through the troposphere. Some regions in the Southern Hemispherehad record or near-record high temperatures for the year. Australia observed its hottest year on record, while Argentina and New Zealand reported their second and third hottest years, respectively. In Antarctica, Amundsen-Scott South Pole Station reported its highest annual temperature since records began in 1957 At the opposite pole, the Arctic observed its seventh warmest year since record's began in the early 20th century. At 20-m depth, record high temperatures were measured at some permafrost stations on the North Slope Of Alaska and in the Brooks Range. In the Northern Hemisphere extratropics, anomalous meridional atmospheric circulation occurred throughout much of the year leading to marked regional extremes of both temperature and precipitation. Cold temperature anomalies during Winter across Eurasia were followed by warm Spring temperature anomalies, which, were linked to a new record Eurasian snow cover extent in the May.Minimum sea ice extent in the :Arctic was the sixth lowest since satellite Observations began in 1979. Including 2013, all seven lowest extents on record have occurred in the past seven years Antarctica, on the other hand, had above average sea ice extent throughout 2013, with 116 days Of new daily high extent records, inclding a new daily maximum sea ice area of 19.57 million km(2) reached on 1 October.ENSO-neutral conditions in the eastern central Pacific Ocean and a negative Pacific decadal oscillation pattern in the North Pacific had the largest impacts on the global sea surface temperature in 2013: The North Pacific reached a historic high temperature in 2013 and on balance the globally-averaged sea surface temperature was among the 10 highest on record. Overall, the salt Content in near-surface ocean waters increased while in intermediate waters it decreased. Global mean sea level continued to rise during 2013, on pace with a trend of 3,2 mm yr(-1) over the past two decades. A portion of this trend (0.5 mm yr(-1)) has been attributed to natural variability associated with the Pacific decadal oscillation as Well as to ongoing contribution from the melting of glaciers and ice sheets and ocean warming.Global tropical cyclone frequency during 2013 was slightly above average with a total of 94 storms, although the North Atlantic Basin had its quietest hurricane season since 1994. In the Western North Pacific Basin, Super Typhoon Haiyan, the deadliest tropical Cyclone of 2013, had 1-minute sustained winds estimated to be 170 kt (OS m s(-1)) on 7 November, the highest Wind speed ever assigned to a tropical cyclone. High storm surge was also associated with Haiyan at it Made landfall over the central Philippines, an area where sea level is currently at historic highs increasing by 200 mm since 1970.In the atmosphere, carbon dioxide, methane, and nitrous oxide all Continued to increase in 2013. As in previous our years, each of these Major greenhouse gases once again reached historic high Concentrations. In the Arctic carbon dioxide and methane:, Increased at the same rate as:the global increase. These increases are likely due to export from lower latitudes rather than a consequence Of increases in Arctic sources such as thawing permafrost., At Mauna Loa, Hawaii, for the first time since measurement began in 1958, the daily average Mixing ratio Of carbon dioxide exceeded 400 ppm on 9 May.The state of these variables, along with dozens of others, and the 2013 climate conditions of regions around the world are discussed in further detail in this 24th, edition of the State of the Climate series.