Precipitation trend for different data sets over various time periods

<b>Table 2.</b> Precipitation trend for different data sets over various time periods. Statistically significant values at the 95% confidence level are marked bold. Δ<em>m</em> denotes the 95% confidence range. Trends from composite model runs are calculated from ensemble means. <strong>Abstract</strong> Global warming is expected to enhance fluxes of fresh water between the surface and atmosphere, causing wet regions to become wetter and dry regions drier, with serious implications for water resource management. Defining the wet and dry regions as the upper 30% and lower 70% of the precipitation totals across the tropics (30° S–30° N) each month we combine observations and climate model simulations to understand changes in the wet and dry regions over the period 1850–2100. Observed decreases in precipitation over dry tropical land (1950–2010) are also simulated by coupled atmosphere–ocean climate models (−0.3%/decade) with trends projected to continue into the 21st century. Discrepancies between observations and simulations over wet land regions since 1950 exist, relating to decadal fluctuations in El Niño southern oscillation, the timing of which is not represented by the coupled simulations. When atmosphere-only simulations are instead driven by observed sea surface temperature they are able to adequately represent this variability over land. Global distributions of precipitation trends are dominated by spatial changes in atmospheric circulation. However, the tendency for already wet regions to become wetter (precipitation increases with warming by 3% K⁻¹ over wet tropical oceans) and the driest regions drier (precipitation decreases of −2% K⁻¹ over dry tropical land regions) emerges over the 21st century in response to the substantial surface warming.

表2. 不同数据集在不同时段的降水趋势。95%置信水平下具有统计学显著性的数值以粗体标注。Δ<em>m</em>表示95%置信区间。合成模式运行得到的趋势由集合平均计算得出。

**摘要** 全球变暖预计将增强地表与大气之间的淡水通量，使得湿润区域愈发湿润、干旱区域愈发干旱，这对水资源管理具有深远影响。本研究将热带区域（南纬30°至北纬30°）内每月降水总量排名前30%的区域定义为湿润区、后70%的区域定义为干旱区，结合观测数据与气候模式模拟结果，分析1850年至2100年间湿润区与干旱区的降水变化。热带干旱陆地区域1950—2010年观测到的降水减少趋势，也被耦合大气-海洋气候模式（coupled atmosphere–ocean climate model）复现（减少速率为-0.3%/十年），且该趋势预计将持续至21世纪。1950年以来，湿润陆地区域的观测与模拟结果存在差异，这与厄尔尼诺-南方涛动（El Niño Southern Oscillation）的年代际波动有关，而耦合模拟未能准确再现该波动的发生时序。若改用观测得到的海表温度（sea surface temperature）驱动仅考虑大气过程的模拟，则该模式能够较好地复现陆地区域的此类变率。全球降水趋势的空间分布主要由大气环流的空间变化主导。不过，随着21世纪地表显著增温，湿润区域愈发湿润、干旱区域愈发干旱的趋势逐渐显现：热带湿润洋面的降水随增温速率为3%·K⁻¹，而热带干旱陆地区域的降水减少速率为-2%·K⁻¹。