Understanding vulnerabilities of continental precipitation to changing climatic conditions is of critical importance to society at large. Terrestrial precipitation is fed by moisture originating as evaporation from oceans and from recycling of water evaporated from continental sources. In this study, continental precipitation and evaporation recycling processes in the Earth system model GFDL-ESM2G are shown to be consistent with estimates from two different reanalysis products. The GFDL-ESM2G simulations of historical and future climate also show that values of continental moisture recycling ratios were systematically higher in the past and will be lower in the future. Global mean recycling ratios decrease 2%–3% with each degree of temperature increase, indicating the increased importance of oceanic evaporation for continental precipitation. Theoretical arguments for recycling changes stem from increasing atmospheric temperatures and evaporative demand that drive increases in evaporation over oceans that are more rapid than those over land as a result of terrestrial soil moisture limitations. Simulated recycling changes are demonstrated to be consistent with these theoretical arguments. A simple prototype describing this theory effectively captures the zonal mean behavior of GFDL-ESM2G. Implications of such behavior are particularly serious in rain-fed agricultural regions where crop yields will become increasingly soil moisture limited.
The deuterium excess (d‐excess) of precipitation varies seasonally at sites across the globe, an observation that has often been linked to seasonal changes in oceanic evaporation conditions, continental moisture recycling, and subcloud raindrop re‐evaporation. However, there have been very few studies to quantify and evaluate the relative importance of these processes. Here, we revisit the mechanisms of precipitation d‐excess seasonality in low‐latitudes and mid‐latitudes through a new analysis of precipitation isotope databases along with climate reanalysis products and moisture tracking models. In low‐latitudes, the raindrop re‐evaporation effect, indicated by local relative humidity, exerts a strong and prevalent control on observed d‐excess seasonality and overprints the effect of oceanic evaporation conditions. In mid‐latitudes, the effect of oceanic evaporation conditions becomes stronger and seems dominant in the observed d‐excess seasonality. However, the ultimate d‐excess signals are produced after complex modulations by several reinforcing or competing processes, including prior distillations, moisture recycling, supersaturation in snow formation, and raindrop re‐evaporation. Among these processes, substantial increases in the proportion of recycled moisture during the warm and dry season do not produce higher precipitation d‐excess in mid‐latitude continental interiors. We develop a simple seasonal water storage model to show that contributions of previously evaporated residual water storage and higher transpiration fractions may lead to relatively low d‐excess in evapotranspiration fluxes during periods of enhanced continental moisture recycling. This study underscores the ubiquitous nonconservative behavior in d‐excess throughout the water cycle, as opposed to using d‐excess as a simple tracer for remote conditions at oceanic moisture sources.
more » « less- NSF-PAR ID:
- 10377167
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Global Biogeochemical Cycles
- Volume:
- 36
- Issue:
- 10
- ISSN:
- 0886-6236
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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