Modeling Spatial Soil Water Dynamics in a Tropical Floodplain, East Africa

Abstract

Analyzing the spatial and temporal distribution of soil moisture is critical for ecohydrological processes and for sustainable water management studies in wetlands. The characterization of soil moisture dynamics and its influencing factors in agriculturally used wetlands pose a challenge in data-scarce regions such as East Africa. High resolution and good-quality time series soil moisture data are rarely available and gaps are frequent due to measurement constraints and device malfunctioning. Soil water models that integrate meteorological conditions and soil water storage may significantly overcome limitations due to data gaps at a point scale. The purpose of this study was to evaluate if the Hydrus-1D model would adequately simulate soil water dynamics at different hydrological zones of a tropical floodplain in Tanzania, to determine controlling factors for wet and dry periods and to assess soil water availability. The zones of the Kilombero floodplain were segmented as riparian, middle, and fringe along a defined transect. The model was satisfactorily calibrated (coefficient of determination; R 2 = 0.54-0.92, root mean square error; RMSE = 0.02-0.11) on a plot scale using measured soil moisture content at soil depths of 10, 20, 30, and 40 cm. Satisfying statistical measures (R 2 = 0.36-0.89, RMSE = 0.03-0.13) were obtained when calibrations for one plot were validated with measured soil moisture for another plot within the same hydrological zone. Results show the transferability of the calibrated Hydrus-1D model to predict soil moisture for other plots with similar hydrological conditions. Soil water storage increased towards the riparian zone, at 262.8 mm/a while actual evapotranspiration was highest (1043.9 mm/a) at the fringe. Overbank flow, precipitation, and groundwater control soil moisture dynamics at the riparian and middle zone, while at the fringe zone, rainfall and lateral flow from mountains control soil moisture during the long rainy seasons. In the dry and short rainy seasons, rainfall, soil properties, and atmospheric demands control soil moisture dynamics at the riparian and middle zone. In addition to these factors, depths to groundwater level control soil moisture variability at the fringe zone. Our results support a better understanding of groundwater-soil water interaction, and provide references for wetland conservation and sustainable agricultural water management.

The Impact of Land Use/Land Cover Change (LULCC) on Water Resources in a Tropical Catchment in Tanzania under Different Climate Change Scenarios

“…The hot spot of change for both scenarios is the fringe of the wetland. However, the center of the wetland is not transformed to agricultural fields on both setups, which is also reasonable due to the extended flooding and the threat to lose the harvest [79]. Other areas of agricultural expansion are the western parts and the central northern parts, near the cities of Makambako and Njombe, and the main roads A104 and B4 (Figure 1).…”

HYDRUS-1D Simulation of Soil Water Dynamics for Sweet Corn under Tropical Rainfed Condition

“…As compared to other models, HYDRUS-1D has the flexibility of accommodating different boundary conditions and the capability to consider the root uptake of water and nutrient simultaneously. The model is capable of simulating soil water and solute dynamics under different management practices [13][14][15][16][17][18][19][20][21][22]. All these researchers validated HYDRUS-1D as a reliable tool for such investigations.…”

Assessing seasonal land cover dynamics in the tropical Kilombero floodplain of East Africa

“…Depth to groundwater was monitored hourly by pressure sensors installed in 10-cm-diameter piezometers at each hydrological position from March 2015 to June 2016. 45 This research included observations from nine piezometers (Fig. 1).…”

“…Rainfall pattern is reflected directly in the fringe piezometers whereas the response in the middle and riparian fields is very little and is delayed. 45 A steep decrease in depth to ground water is observed in March and January, usually taking between 1 and 2 months to reach a peak. A slight increase in depth to groundwater is observed in February coinciding with the reduced precipitation.…”

“…The Kilombero River drives the groundwater in the southern part whereas lateral flow from the Udzungwa Mountains drives the groundwater in northern part. 45 Floods are variable and discernable on the optical images. Lateral flow is deep-seated and more stable.…”