Groundwater convergence as a possible mechanism for multi‐year persistence in rainfall

Abstract

Yearly rainfall totals in wet‐to‐dry climate transition zones show marked multiyear periods of dry and wet anomalies. These are said to originate from large‐scale external forcings (e.g. SST anomalies) and enhanced by land‐atmosphere coupling through soil moisture, vegetation and surface albedo. We explore the hypothesis that the degree of persistence in rainfall may be partly caused by groundwater convergence, i.e. the confluence of groundwater to discharge zones that remain wet throughout the year to sustain evaporation for longer periods of time. A simple stochastic model of soil moisture‐precipitation feedback augmented with a groundwater component shows that groundwater convergence introduces long‐term persistence in rainfall. The degree of persistence (as measured by the Hurst exponent of simulated yearly rainfall totals) increases with groundwater residence time. This notion has important ramifications for multiyear drought forecasting, whereby monitoring or concurrent modeling of groundwater stores may play a role in improving predictability.

Validation of terrestrial water storage variations as simulated by different global numerical models with GRACE satellite observations

“…Snow cover raises surface albedo and isolates the land surface from the atmosphere. Groundwater also shows a significant lowfrequency variability that could have regional impacts on inter-annual climate variability (Bierkens and van den Hurk, 2007). Monitoring data on water availability from both in situ and remote sensing instruments are also essential for economic and societal development.…”

A global-scale two-layer transient groundwater model: development and application to groundwater depletion

“…Bierkens and van den Hurk, 2007;de Graaf et al, 2013;Wada et al, 2014). Moreover, groundwater often flows across topographical and administrative boundaries at considerable rates, supporting water budgets of receiving catchments or aquifers (Schaller and Fan, 2009).…”

Spatial cross‐correlation patterns of European low, mean and high flows

“…Questions of specific interest may be directed to the identification of (quasi) periodic phenomena and the influence of large-scale atmospheric circulation patterns. In recent years, the feedback between terrestrial water storage and atmospheric variability has received increasing attention [Bierkens and van den Hurk , 2007;Seneviratne et al, 2010]. In this context, it may be of interest to assess whether runoff observations from a large number of small catchments can provide added information that may assist to fully understand the influence of land-atmosphere interactions on climate variability.…”

“…persistence) in hydrological time series. Amongst these are climate instationarities [Potter , 1976] -possibly due to landatmosphere interactions [Bierkens and van den Hurk , 2007] -, storage mechanisms [Klemeš, 1974], groundwater upwelling , and channel routing [Mudelsee, 2007].…”