Hydrologic responses to projected climate change in ecologically diverse watersheds of the Gulf Coast, United States

Abstract

The Gulf Coast watersheds in the United States contain some of the highest levels of biodiversity of all freshwater systems in North America. Developing environmental management policies to protect and preserve these ecosystems makes the study of the impacts of projected climate change on the future hydrologic cycle crucial. We used the Soil and Water Assessment Tool (SWAT) to estimate the potential hydrologic changes for the mid-21st century (2050s) and the late 21st century (2080s) in the Mobile River, Apalachicola River, and Suwannee River watersheds in the Gulf Coast region of the United States. These estimates are based on downscaled future climate projections from 20 global circulation models (GCMs) under two representative concentration pathways (RCPs 4.5 and 8.5). SWAT models were calibrated and validated using the multi-algorithm, genetically adaptive multi-objective (AMALGAM) technique in a high-performance computing (HPC) cluster. For the Gulf Coast watersheds, the climate is projected to be warmer and wetter. Projected changes in climatic variables are likely to bring large changes in both annual and seasonal hydrologic processes within these watersheds. We found substantial decreases in mean annual streamflow under RCP8.5 during the 2080s, with up to a 13.0% decrease projected for the Suwannee River watershed compared to the present day. Summer streamflow is projected to be substantially lower during the 2080s, with up to a 25.1% decrease projected for the Suwannee River watershed, during a time of high demand of water resources for agricultural, industrial, and ecosystem services. These hydrologic projections are expected to help in making better-informed decisions for future water resources and ecosystem management in the Gulf Coast region.

Choosing an arbitrary calibration period for hydrologic models: How much does it influence water balance simulations?

“…Late summer and fall precipitation were typically lower in the St. Joseph River watershed in earlier calibration periods as well, for instance mean September precipitation was only 67 mm with the 33-67 C/V strategy (1950)(1951)(1952)(1953)(1954)(1955)(1956)(1957)(1958)(1959)(1960)(1961)(1962)(1963)(1964)(1965)(1966) but 90 mm with the 67-33 V/C strategy (1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999) S5; Tables S6-S8 in Data S1). These parameters were found to be appropriate in previous work (Feyereisen et al, 2007;Ficklin et al, 2012;Mehan et al, 2016;Neupane et al, 2018;Singh et al, 2013) The six strategies for the temporal split-sample approach were calibrated individually for each watershed at the daily time step, with a total of 3200 function evaluations each. The simulation that had the highest NSE for each strategy was considered to be the optimized simulation.…”

Exploring Impacts of River Discharge on Forage Fish and Predators Using Ecopath With Ecosim

“…Two sets of future flow projections, short-term and long-term, were made to understand the impact of discharge on fish biomass. We explored the ecological impacts of the future discharge projections made by Neupane et al (2019) on the Suwannee River Estuary using Ecopath with Ecosim. In addition to the longterm climate projections from Neupane et al (2019), a series of short-term (three-year) flow scenarios was tested to determine the impact of anomalous flood and drought conditions.…”

“…Since 1975, human population growth in the region has been considerable and the impacts of this population growth may be seen in the increase in irrigation intensive agricultural (see Marella et al, 2016). Regarding climatic impacts, changes in both precipitation and evapotranspiration have been projected for the area, which will likely impact discharge (Swain and Davis, 2016;Neupane et al, 2019). Swain and Davis (2016) estimated a ∼5% increase in evapotranspiration between the years 2039 and 2069, and Neupane et al (2019) forecasted a 12% increase for the 2080s under a high emissions scenario.…”

“…Regarding climatic impacts, changes in both precipitation and evapotranspiration have been projected for the area, which will likely impact discharge (Swain and Davis, 2016;Neupane et al, 2019). Swain and Davis (2016) estimated a ∼5% increase in evapotranspiration between the years 2039 and 2069, and Neupane et al (2019) forecasted a 12% increase for the 2080s under a high emissions scenario. The latter authors also estimated a decrease of 13% in mean discharge for the Suwannee with a 25.1% decrease during summer when anthropogenic water demands are high.…”

Multispecies conservation of freshwater fish assemblages in response to climate change in the southeastern United States

“…The Mobile River Basin (MRB), located in the southeastern United States, contains some of the highest levels of temperate biodiversity in North America, including many endemic species (Benke & Cushing, ). However, the MRB is expected to experience dramatic increases in water temperature and decreases in summer streamflow as a result of ongoing changes in climate (Neupane, Ficklin, Knouft, Ehsani, & Cibin, ; van Vliet et al, ). Because of the high level of biodiversity and the projected changes to hydrologic and thermal conditions in the region, there is an urgent need to evaluate potential responses of freshwater fish biodiversity to these alterations in environmental conditions and to identify areas that may provide refuge from climate‐induced habitat alterations.…”