Abstract
Abstract. Satellite-based data, such as vegetation type and fractional vegetation cover, are widely used in hydrologic models to prescribe the vegetation state in a study region. Dynamic global vegetation models (DGVM) simulate land surface hydrology. Incorporation of satellite-based data into a DGVM may enhance a model's ability to simulate land surface hydrology by reducing the task of model parameterization and providing distributed information on land characteristics. The objectives of this study are to (i) modify a DGVM for simulating land surface water balances; (ii) evaluate the modified model in simulating actual evapotranspiration (ET), soil moisture, and surface runoff at regional or watershed scales; and (iii) gain insight into the ability of both the original and modified model to simulate large spatial scale land surface hydrology. To achieve these objectives, we introduce the "LPJ-hydrology" (LH) model which incorporates satellite-based data into the Lund-Potsdam-Jena (LPJ) DGVM. To evaluate the model we ran LH using historical (1981–2006) climate data and satellite-based land covers at 2.5 arc-min grid cells for the conterminous US and for the entire world using coarser climate and land cover data. We evaluated the simulated ET, soil moisture, and surface runoff using a set of observed or simulated data at different spatial scales. Our results demonstrate that spatial patterns of LH-simulated annual ET and surface runoff are in accordance with previously published data for the US; LH-modeled monthly stream flow for 12 major rivers in the US was consistent with observed values respectively during the years 1981–2006 (R2 > 0.46, p < 0.01; Nash-Sutcliffe Coefficient > 0.52). The modeled mean annual discharges for 10 major rivers worldwide also agreed well (differences < 15%) with observed values for these rivers. Compared to a degree-day method for snowmelt computation, the addition of the solar radiation effect on snowmelt enabled LH to better simulate monthly stream flow in winter and early spring for rivers located at mid-to-high latitudes. In addition, LH-modeled monthly soil moisture for the state of Illinois (US) agreed well (R2 = 0.79, p < 0.01) with observed data for the years 1984–2001. Overall, this study justifies both the feasibility of incorporating satellite-based land covers into a DGVM and the reliability of LH to simulate land-surface water balances. To better estimate surface/river runoff at mid-to-high latitudes, we recommended that LPJ-DGVM considers the effects of solar radiation on snowmelt.
Highlights
Evapotranspiration (ET), soil moisture, and surface runoff are three major components of the hydrologic cycle at the land surface, and affect many important processes in the soil-vegetation-atmosphere system (Lu et al, 2003; Murphy and Lodge, 2004)
Because less snowmelt was simulated under the degree-day method in winter and early spring, the subsequent monthly stream flow was much higher than observed values in late spring in these watersheds where heavy snow occurs in winter and spring
LH is developed by incorporating satellite-based land covers and proportional foliar vegetation covers into LPJ-Dynamic global vegetation models (DGVM) (Sitch et al, 2003; Gerten et al, 2004) for simulating land surface water balances at the regional scale
Summary
Evapotranspiration (ET), soil moisture, and surface runoff are three major components of the hydrologic cycle at the land surface, and affect many important processes in the soil-vegetation-atmosphere system (Lu et al, 2003; Murphy and Lodge, 2004). Soil-moisture deficits can restrict the respiration and the productivity of plants, and influence species composition as well as type and structure of vegetation (Evans and Trevisan, 1995; Brabson et al, 2005). Shifts in surface runoff influence the ability of regional water. J. Bartlein: Modifying a DGVM for water-balance simulation supply and demand as well as the cycling of nutrients globally. The importance of ET, soil moisture, and surface runoff for human well-being, terrestrial ecosystems, and agricultural sustainability requires that we be able to simulate landsurface water balances, especially given that the global hydrological cycle is expected to intensify in response to ongoing climate change The importance of ET, soil moisture, and surface runoff for human well-being, terrestrial ecosystems, and agricultural sustainability requires that we be able to simulate landsurface water balances, especially given that the global hydrological cycle is expected to intensify in response to ongoing climate change (e.g. Murray et al, 2011)
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