Influence of landscape heterogeneity on water available to tropical forests in an Amazonian catchment and implications for modeling drought response

Abstract

The Amazon basin has experienced periodic droughts in the past, and intense and frequent droughts are predicted in the future. Landscape heterogeneity could play an important role in how tropical forests respond to drought by influencing water available to plants. Using the one‐dimensional ACME Land Model and the three‐dimensional ParFlow variably saturated flow model, numerical experiments were performed for a catchment in central Amazon to elucidate processes that influence water available for plant use and provide insights for improving Earth system models. Results from ParFlow show that topography has a dominant influence on groundwater table and runoff through lateral flow. Without any representations of lateral processes, ALM simulates very different seasonal variations in groundwater table and runoff compared to ParFlow even if it is able to reproduce the long‐term spatial average groundwater table of ParFlow through simple parameter calibration. In the ParFlow simulations, even in the plateau with much deeper water table depth during the dry season in the drought year of 2005, plant transpiration is not water stressed as the soil saturation is still sufficient for the stomata to be fully open based on the empirical wilting formulation in the models. This finding is insensitive to uncertainty in atmospheric forcing and soil parameters, but the empirical wilting formulation is an important factor that should be addressed using observations and modeling of coupled plant hydraulics‐soil hydrology processes in future studies. The results could be applicable to other catchments in the Amazon basin with similar seasonal variability and hydrologic regimes.

Coupling a three-dimensional subsurface flow and transport model with a land surface model to simulate stream–aquifer–land interactions (CP v1.0)

“…By misrepresenting, or not including, key hydrologic processes on the scale of interest, CLM4.5 fails to capture groundwater table dynamics, which could propagate to water and energy budgets and have profound impacts on boundary layer, convection, and cloud formation in coupled land-atmosphere studies. Our finding is consistent with results from other recent studies in which integrated surface and subsurface models were compared to standalone land surface models (Fang et al, 2017;Niu et al, 2017).…”

Why Do Large‐Scale Land Surface Models Produce a Low Ratio of Transpiration to Evapotranspiration?

“…We use a terrestrial integrated modeling system (TIMS, Niu et al, ) in this study to investigate major factors controlling the ET partitioning. TIMS integrates the water flow model of CATHY (CATchment HYdrology, Camporese et al, ), the Noah‐MP LSM (Niu et al, ), a radiation correction model (Fang et al, ), and a six‐carbon pool microbial enzyme model (Zhang et al, ).…”

“…In turn, these impacts may propagate into the atmospheric boundary layer, affecting the planetary boundary layer height, air temperature, convective available potential energy, and convection precipitation (e.g., Gilbert et al, ; Keune et al, ; Maxwell et al, ; Rahman et al, ; Rihani et al, ). A growing body of literature also suggests that lateral subsurface flow can substantially enhance the T / ET ratio (Fang et al, ; Maxwell & Condon, ), and this effect becomes slightly more significant for higher model resolutions (Shrestha et al, ).…”

Distributed Plant Hydraulic and Hydrological Modeling to Understand the Susceptibility of Riparian Woodland Trees to Drought‐Induced Mortality

“…Advances in understanding plant response to atmospheric drought highlight the need for improvements in describing belowground processes that mediate water availability (Billings, ; Fang et al, ; Phillips et al, ). In addition to precipitation infiltration from the top, soils can also be wetted from below or laterally through groundwater processes at local, landscape, and regional scales (Figure ).…”

“…The impacts of drought on ecosystems can be diverse (Bond et al, 2008), and it is challenging for ecosystem models to predict plant responses to drought (Powell et al, 2013). This can be attributed in part to oversimplified representations of both plant responses to soil drying (Fisher et al, 2017;McDowell et al, 2013) and heterogeneous plant water supply across the landscape (J. S. Clark et al, 2016;Fang et al, 2017).…”