Potential negative effects of groundwater dynamics on dry season convection in the Amazon River basin
Yen‑Heng Lin1 · Min‑Hui Lo1 · Chia Chou1,2
Received: 5 November 2014 / Accepted: 22 April 2015 © The Author(s) 2015. This article is published with open access at Springerlink.com
Keywords Groundwater · Amazon River basin ·
Moist static energy 1 Introduction
The need to incorporate groundwater hydrology in global land surface models is receiving increased attention (Liang et al. 2003; Yeh and Eltahir 2005; Niu et al. 2007; Fan et al. 2007; Lo et al. 2008, 2010; Campoy et al. 2013; Krakauer et al. 2013). Groundwater storage can affect atmospheric and terrestrial hydrological processes by affecting soil moisture profiles and evapotranspiration (ET) rates (Famiglietti and Wood 1994; Gutowski et al. 2002; Yeh and Famiglietti 2009). For example, partitioning precipitation into ET and runoff can be considerably improved after incorporating water table dynamics in land surface model parameterization (Yeh and Eltahir 2005). Hasler and
Avissar (2007) mentioned that general circulation models (GCMs) often overestimate the water stress in tropical rain forests. After including groundwater storage in aquifers, simulated total land water storage anomalies (including soil water and groundwater) more closely matched those observed in the Gravity Recovery and Climate Experiment [GRACE, Tapley et al. (2004)] in regions where snow melt and frozen soils are not dominant (Niu et al. 2007).
A study conducted using an observational data set including soil moisture, groundwater, and streamflow showed that groundwater storage can have a substantial impact on the rate of ET, especially during dry seasons in Illinois (Yeh and Famiglietti 2009). Based on extensive collections of groundwater well data sets, Fan et al. (2013) concluded that on a global basis, shallow groundwater influences approximately 27 % of the global land area, including approximately 15 % of groundwater-fed surface water regions.
Abstract Adding a groundwater component to land surface models affects modeled precipitation. The additional water supply from the subsurface contributes to increased water vapor in the atmosphere, resulting in modifications of atmospheric convection. This study focuses on how groundwater dynamics affect atmospheric convection in the
Amazon River basin (ARB) during July, typically the driest month. Coupled groundwater–land–atmosphere model simulations show that groundwater storage increases evapotranspiration rates (latent heat fluxes) and lowers surface temperatures, which increases the surface pressure gradient and thus, anomalous surface divergence. Therefore, the convection over the Southern Hemispheric ARB during the dry season becomes weaker when groundwater dynamics are included in the model. Additionally, the changes in atmospheric vertical water vapor advection are associated with decreases in precipitation that results from downwelling transport anomalies. The results of this study highlight the importance of subsurface hydrological processes in the Amazon climate system, with implications for precipitation changes during the dry season, observed in most current climate models. * Min-Hui Lo firstname.lastname@example.org
Yen-Heng Lin email@example.com
Chia Chou firstname.lastname@example.org 1
Department of Atmospheric Sciences, National Taiwan
University, Taipei, Taiwan 2
Research Center for Environment Changes, Academia Sinica,
Y.-H. Lin et al. 1 3
Groundwater storage can also influence climate at regional and global scales. Some studies (Anyah et al. 2008; Yuan et al. 2008; Jiang et al. 2009; Campoy et al. 2013) have shown that accounting for hydrological processes in aquifers and lower soil boundary conditions can alter simulated land–atmosphere feedbacks in regional and global climate models. Including a groundwater module in land surface models alters the modeled distribution of precipitation (Lo and Famiglietti 2011). Their results indicated that globally inhomogeneous changes in precipitation in the boreal summer, and tropical regions show a positive anomaly in the Northern Hemisphere and a negative anomaly in the Southern Hemisphere. In addition to directly supplying water to the soil, atmosphere, and surface water, groundwater storage may also modulate the timescales of terrestrial hydrological processes because of the long time scales involved. van den Hurk et al. (2005) found that the responses of the terrestrial hydrological cycle are usually too rapid in regional models because of insufficient land water storage. Similarly, Koutsoyiannis et al. (2007) showed that simulated runoff has a high temporal persistence when groundwater storage is incorporated into the runoff generation scheme. Groundwater storage can have nonlinear effects on the surface soil moisture persistence, depending on water table dynamics (Lo and Famiglietti 2010). Including a groundwater aquifer module to the Goddard Institute for Space Studies (GISS) ModelE general circulation model had a limited impact on mean climate, but affected the seasonality and interannual persistence of soil moisture and climate (Krakauer et al. 2013).
From a regional perspective, groundwater storage also plays a critical role in the hydrological cycle in the Amazon River basin (ARB), which contributes a substantial amount of water vapor to the atmosphere and fresh water discharge to the ocean. Because of the delayed response of groundwater to atmospheric forcing, groundwater storage can provide a buffer for the surface water dynamics in the Amazon River in dry seasons Miguez-Macho and Fan (2012a). Miguez-Macho and Fan (2012b) also suggested that accounting for shallow groundwater produces considerable differences in the simulated soil moisture over the ARB. The response of ET to groundwater depends on the seasonal amplitude of the atmospheric precipitation and temperature, and land surface conditions, resulting in a substantial increase in ET in the dry season. Using an observational dataset, Juárez et al. (2007) showed that, during the dry season, the deep soil provides a sufficient supply of water to account for ET because of the extensive and deep root system of trees in the ARB (da Rocha et al. 2009). Hydraulic redistribution (HR), a phenomenon of tree root redistributes soil water from wet to dry areas at night and normally redistributes the water from deep soil, where water was stored in raining season, to surface soil (Lee et al. 2005). Lee et al. (2005) have shown that HR can influence ET and surface temperature in the dry season, because the redistribution of water enhances the transpiration and lowers the surface temperature.