What Are the Implications of Global Warming for Precipitation and Water Availability?

What Are the Implications of Global Warming for Precipitation and Water Availability?

So what does all this human-induced warming mean for the water cycle and water availability? Thinking back to module 2, you learned that warmer air can hold more water (i.e., warmer air has a higher saturation vapor pressure). Therefore it is reasonable to expect higher amounts of water vapor in the air. This is supported by observations that show a 3.5% increase in water vapor in the past 40 years as the climate has warmed about 0.5°C, with relative humidity remaining approximately constant.

Changes in precipitation are harder to measure (or predict) compared with changes in atmospheric water vapor content because of the immense temporal and spatial variability of precipitation. Nevertheless, patterns of precipitation change can readily be observed from historical records (Figure 2), with many areas seeing increases greater than 25 mm/year per decade (i.e., going from 300 mm/yr to 325 mm/yr over the course of a decade) and other places (particularly Africa and Southeast Asia) seeing decreases in precipitation at rates greater than 10 to 25 mm/year per decade. With increasing temperatures, it naturally follows that a greater proportion of precipitation would fall as rain, rather than snow, which has also been documented by the IPCC.

Figure 2. (IPCC Chapter 2, Figure 2.15) Maps of observed precipitation change over land from 1901-2019 (panels (a) and (b)) from the Climate Research Unit (CRU, top), Global Precipitation Climatology Center (GPCC, middle). Map of observed precipitation change over land from 1980-2019 (panels (d) and (e)) from same sources. Panel (c) shows global land precipitation anomalies and panel (f) shows globally complete precipitation data from the Global Precipitation Climatology Project (GPCP). More information is found in the supplemental section of chapter 2.

Source: IPCC, 2019