| Summary: | 碩士 === 國立臺灣大學 === 大氣科學研究所 === 103 === Terrestrial water storage (TWS) is a fundamental signal in the land hydrological cycle, and its changes play a crucial role in the earth’s climate system. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) has offered a new method to estimate the variability of TWS by measuring gravity changes, in which GRACE can provide for the first time the TWS globally at monthly time scales.
In this study, we used simulations from the Coupled Model Intercomparison Project Phase 5 (CMIP5) archives to investigate changes in the annual range of soil water storage under global warming. Results show that future warming could lead to significant declines in snowfall, and a corresponding lack of snowmelt water recharge to the soil, which makes soil water less available during spring and summer. Conversely, more precipitation as rainfall results in higher recharge to soil water during its accumulating season. Thus, the wettest month of soil water gets wetter, and the driest month gets drier, resulting in an increase of the annual range and suggesting that stronger heterogeneity in global water distribution (changing extremes) could occur under global warming. This has implications for water management and water security under a changing climate.
In addition, we compared the GRACE data with the results of TWS simulated by several land surface models over Australia, where lots of dry and endorheic basins exist with low frequencies of water mass changes. We examined several factors and mechanisms that cause the bias between models and observations. Since land surface models provide the boundary conditions for the land-atmosphere interaction in the global climate models, the mechanisms whereby water transport influences terrestrial water storage might impact the climate. Furthermore, the highly spatial and temporal variability in water storage over Australia plays an essential role in affecting the variability of land-atmosphere coupling strength. In this study, we applied an index to diagnose the impacts of variabilities in water storage on the coupling strength. Results show that the sensitivity index first increases but then decreases during the flooding in semi-arid regions, which is the temporal transition between the soil moisture-limited regime and the energy-limited regime. The high sensitivity index indicates that the evaporation follows well with soil moisture variations, while the low sensitivity index reveals weaker land-atmosphere interactions. Therefore, the results have crucial implications for land-atmosphere interactions and climate predictions.
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