Abstract
Abstract. Floodplains play an important role in the terrestrial water cycle and are very important for biodiversity. Therefore, an improved representation of the dynamics of floodplain water flows and storage in global hydrological and land surface models is required. To support model validation, we combined monthly time series of satellite-derived inundation areas (Papa et al., 2010) with data on irrigated rice areas (Portmann et al., 2010). In this way, we obtained global-scale time series of naturally inundated areas (NIA), with monthly values of inundation extent during 1993–2004 and a spatial resolution of 0.5°. For most grid cells (0.5°×0.5°), the mean annual maximum of NIA agrees well with the static open water extent of the Global Lakes and Wetlands database (GLWD) (Lehner and Döll, 2004), but in 16% of the cells NIA is larger than GLWD. In some regions, like Northwestern Europe, NIA clearly overestimates inundated areas, probably because of confounding very wet soils with inundated areas. In other areas, such as South Asia, it is likely that NIA can help to enhance GLWD. NIA data will be very useful for developing and validating a floodplain modeling algorithm for the global hydrological model WGHM. For example, we found that monthly NIAs correlate with observed river discharges.
Highlights
Wetlands play an important role in the terrestrial water cycle, influencing evapotranspiration, water storage and river discharge dynamics
To obtain time series of naturally inundated areas (NIA) that can serve as a basis for validating modeled floodplain inundation dynamics, the extent of irrigated rice as estimated in the MIRCA2000 data set by Portmann et al (2010) was subtracted from the 1993– 2004 time series of monthly satellite-derived inundated areas
In order to support the improved modeling of floodplain inundation in the global hydrological model WGHM, we combined a multisatellite data set of inundated areas (Papa et al, 2010) for the time period 1993–2004 with data on monthly irrigated rice areas around the year 2000 (Portmann et al, 2010)
Summary
While the models of Decharme et al (2008) and Coe et al (2008) aim at simulating the inundation of floodplains that occurs when river channels can no longer contain all the flowing water, the WaterGAP Global Hydrology Model WGHM (Doll et al, 2003), with a spatial resolution of 0.5◦×0.5◦, simulates all types of inland wetlands (including floodplains, freshwater marshes, swamp forests, bogs, fens and salt pans) but does not distinguish among the different types. Compared to seasonal water storage variations as obtained from satellite-derived gravity fields, WGHM underestimates the amplitude of the seasonal water storage variations in the Amazon basin (Fiedler and Doll, 2010; Werth and Guntner, 2010). If the river flow velocity is increased by a factor of 3 (or more, depending on the discharge station), a good agreement between observed and simulated seasonality of river discharge and water storage is obtained This indicates that WGHM might underestimate the storage capacity of the wetlands in the Amazon, and is a motivation for improving the dynamic modeling of wetlands in WGHM, in particular the modeling of floodplains and other wetlands which depend on seasonal river flooding.
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