Quantifying Asynchronicity of Precipitation and Potential Evapotranspiration in Mediterranean Climates

Abstract

Recent climate change has contributed to shifts in the seasonal interplay between precipitation and potential evapotranspiration, which have in turn increased droughts and reduced freshwater availability in Mediterranean climate regions. To overcome limitations in existing indices for comparing these seasonal hydroclimatic drivers at the global scale, we introduce an information theory-based, nonparametric asynchronicity index that captures both the temporal alignment and relative magnitudes of precipitation and potential evapotranspiration. We use this asynchronicity index to first identify Mediterranean climates around the world. We then apply the asynchronicity index over two Mediterranean climate regions and show that their boundaries have shifted between 1960 and 2018, resulting in a regional expansion in the U.S. Pacific Northwest and a contraction in southwestern Australia. These results highlight the need for globally consistent measures of seasonal climatic water supply and demand for diagnosing potential changes in water resources and ecosystem responses within Mediterranean climate regions. Plain Language Summary Climate change is likely to change the boundaries of what aretypically considered Mediterranean climate regions, which have dry summers and mild, wet winters. To analyze how these regions' water availability may be influenced by climate change, we introduce a metric for quantifying the mismatch in the timing and amount of precipitation relative to atmospheric water demand. This new metric is able to identify the boundaries of Mediterranean climate regions more effectively than other existing indices and can be used to analyze how these boundaries shift over time.

Storage in South‐Eastern Australian Catchments

“…Analysis of distinct wet and dry periods may reveal changes in storage behavior and should be a focus of further work. A similar phenomenon has been observed in regions with Mediterranean climates, where the sharp seasonal differences in precipitation and temperature in combination with drought resulted in complex runoff, evapotranspiration, and storage partitioning behavior (Avanzi et al., 2020; Feng et al., 2019; Hahm et al., 2019). Progress in this area is critical, as hydrological models also frequently perform poorly under changing climate scenarios (e.g., Avanzi et al., 2020; Duethmann et al., 2020; Fowler et al., 2016), and more realistic concepts of storage and release behavior need to be integrated into model structures (Fowler et al., 2020).…”

Climate elasticity of evapotranspiration shifts the water balance of Mediterranean climates during multi-year droughts

“…Regions with a Mediterranean climate receive the bulk of precipitation during winter, while summers are dry (Klos et al, 2018). This seasonal imbalance in precipitation distribution, coupled with asynchronicity between precipitation input and potential-evapotranspiration demand (Fellows and Goulden, 2017;Rungee et al, 2018;Feng et al, 2019), complicates understanding and management of multi-year droughts and their impact on water supply (He et al, 2017). Water supply is the output of a water balance, that is, Q = P − ET − S, where Q is runoff, P is precipitation, ET is evapotranspiration, and S is the change in storage (in this paper, it is assumed that S is predominantly dictated by sub-surface storage).…”

CAMELS-BR: hydrometeorological time series and landscape attributes for 897 catchments in Brazil

“…Second, we did not check for temporal dependencies of consecutive high-or low-flow events, for example when two flood peaks occur within a couple of days from each other and both may be related to a single extreme precipitation event. Many criteria exist to identify independent high-flow events (Hall et al, 2014;Archfield et al, 2016) and low-flow events (Fleig et al, 2006;Van Loon, 2015), which might lead to differences in the analyzed signatures.…”