Influence of climate change on water balance of the lowlands of southeastern Peru

<p>The rainforest of the Amazon basin is considered a biodiversity hotspot, and particularly the low-lying rainforest in southeastern Peru in the department of Madre de Dios. This is obtained by the combination of several different climatic zones and by the heterogeneous weather, related to the transition from the complex topography of the Andes to the rainforest in the lowlands. This ecosystem provides the necessary food and raw materials needed by the local communities. Hence, it is important to understand how the regional to local climate, and particularly, precipitation amounts and patterns will change under global warming. To investigate this, the Weather Research and Forecasting (WRF) model version 3.8.1 is employed to downscale 30-year periods for both present and future climates, obtained by the Community Earth System Model (CESM). The years 1981&#8211;2010 are downscaled for the present, while the years 2071&#8211;2100 are selected for the future simulation under the high-emission scenario RCP8.5.</p><p>Our climate simulation shows that precipitation in Madre de Dios will reduce by around 50-100 mm per month during the wetter months October to March. This reduction accounts for around 30 % of the monthly accumulated precipitation of these months. In April to September, the driest months, a decrease of around 20-50 mm is projected. Especially the decline in precipitation in the driest months has important implications since it could mean that precipitation is completely absent for some of the months. In contrast, along the western slopes of the Andes precipitation is projected to increase during the rainy season by around 75-150 mm per month, whereas drying trends are projected for the remaining months. The projected reductions in precipitation over the rainforest in Madre de Dios influence also temperature, causing more extreme values due to stronger heating effects. The climate simulation projects an increase of 2-3 &#176;C during the rainy season, and 3-4 &#176;C during the dry season. The variability of temperature is also larger in the future compared to the present over Madre de Dios.</p><p>The combination of a decrease in humidity and an increase in temperature will exacerbate the risk of fire in the region. To evaluate this risk, the fire weather index (FWI) is calculated, which classifies fire danger into six categories from &#8220;very low&#8221; to &#8220;extreme&#8221;. The FWI is &#8220;very high&#8221; occasionally from July to September in the present, while in the future this level is already reached in June. In both climatic periods the month with the largest fire risk is August, but in the future the risk is increased from &#8220;very high&#8221; to &#8220;extreme&#8221;. This confirms the threat of burning large areas unintendedly, particularly during the transformation of rainforest into agricultural land.</p>