Spatial structure of precipitation anomaly trend (left column) and trend difference relating to changes in precipitation intensity distribution (right column) from ((a), (e)) GPCP, ((b), (f)) AMIP5, ((c), (g)) CMIP historical and ((d), (h)) RCP 4.5 data sets
Figure 4. Spatial structure of precipitation anomaly trend (left column) and trend difference relating to changes in precipitation intensity distribution (right column) from ((a), (e)) GPCP, ((b), (f)) AMIP5, ((c), (g)) CMIP historical and ((d), (h)) RCP 4.5 data sets. The dry tropical oceans are marked with black dots and the dry tropical land with magenta dots (defined as the 70% lowest P grid points for the tropical oceans and the tropical land respectively using the 1988–2005 mean). Trends (%/decade) are calculated over 1988–2008 for GPCP and AMIP5 data sets, 1979–2005 for CMIP5 historical data and 2006–2055 for RCP 4.5 data set. Please note the non-linear colour bars.
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.