Accurate estimates of infiltration and groundwater recharge are critical for many hydrologic, agricultural and environmental applications. Anticipated climate change in many regions of the world, especially in tropical areas, is expected to increase the frequency of high-intensity, short-duration precipitation events, which in turn will affect the groundwater recharge rate. Estimates of recharge are often obtained using monthly or even annually averaged meteorological time series data. In this study we employed the HYDRUS-1D software package to assess the sensitivity of groundwater recharge calculations to using meteorological time series of different temporal resolutions (i.e., hourly, daily, weekly, monthly and yearly averaged precipitation and potential evaporation rates). Calculations were applied to three sites in Brazil having different climatological conditions: a tropical savanna (the Cerrado), a humid subtropical area (the temperate southern part of Brazil), and a very wet tropical area (Amazonia). To simplify our current analysis, we did not consider any land use effects by ignoring root water uptake. Temporal averaging of meteorological data was found to lead to significant bias in predictions of groundwater recharge, with much greater estimated recharge rates in case of very uneven temporal rainfall distributions during the year involving distinct wet and dry seasons. For example, at the Cerrado site, using daily averaged data produced recharge rates of up to 9 times greater than using yearly averaged data. In all cases, an increase in the time of averaging of meteorological data led to lower estimates of groundwater recharge, especially at sites having coarse-textured soils. Our results show that temporal averaging limits the ability of simulations to predict deep penetration of moisture in response to precipitation, so that water remains in the upper part of the vadose zone subject to upward flow and evaporation.
11 Figures and Tables
Fig. 1. Location of the three meteorological sites in Brazil (adapted from an image mask from the IBGE site (ftp://geoftp.ibge.gov.br/mapas_interativos/) using Google Earth Software).
Table 1. Soil hydraulic parameters in Eqs. (1) and (2) for the three soils used in the simulations.
Figure 2. Observed daily precipitation and calculated daily potential evaporation rates for the Cerrado, Temperate and Amazonia sites.
Table 2. Statistical parameters of recharge rates at the Cerrado site as obtained with daily, monthly, and yearly averaged meteorological data.
Fig. 3. Time series of groundwater recharge rates obtained using daily, monthly, and yearly averaged meteorological data from the Cerrado site. Please note the different scales for the daily and monthly data (left side) and the yearly data (right side).
Table 3. Calculated recharge rates as a percentage of rainfall at the Brazilian Cerrado, Temperate and Amazonia sites.
Fig. 4. Box-and-whisker plots and statistical parameters of groundwater recharge rates obtained using daily, monthly, and yearly averaged meteorological data from the Cerrado site, as calculated using the time series shown in Figure 3.
Fig. 5. Cumulative distributions of groundwater recharge rates obtained using daily, monthly, and yearly averaged meteorological data from the Cerrado site (the table shows results of the Kolmogorov-Smirnov test).
Fig. 6. Comparison of daily groundwater recharge for three sites, demonstrating different temporal seasonal patterns, depending on meteorological conditions at the sites.
Fig. 8. Calculated average annual recharge rates at the Cerrado (top), Temperate (middle) and Amazonia (bottom) sites as obtained using daily, monthly, and yearly averaged meteorological data.
Fig. 10. HYDRUS-1D calculated cumulative recharge rates obtained with hourly and daily data for the loam (top) and clay loam (bottom) soils with and without ponding.
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