Multi-scale modeling of water resources in a tropical inland valley and a tropical floodplain catchment in East Africa

This study investigated the dynamics of hydrological processes at the wetland-catchment scale through field scale-based analysis, point scale modeling using Hydrus-1D model along a floodplain transect in Tanzania and wetland-catchment modeling with SWAT model in an inland valley in Uganda. The impact of different land use management options and the projected climate change on the water resources of the inland valley were also evaluated using a hydrological response unit (HRU)-based (ArcSWAT2012) and a grid-based setup (SWATgrid) of the SWAT model. The inland valley is located in Namulonge, central Uganda, and it is one of the headwater catchments of Lake Kyoga basin. The inland valley catchment covers an area of 31 km2 with a wetland area of 4.5 km2. The floodplain is located in Kilombero district, Southern Tanzania and the catchment area is 40,240 km2 and the study area in a wetland is 96 km2. Both sites reflect the prevailing diversity of wetland attributes and uses. Monitoring of hydro-meteorological data for both sites was conducted for two hydrological consecutive years of 2015 and 2016. The cross–section of the wetland transect was subdivided into three major hydrological positions defined as riparian zone, middle, and fringe. Hydrological instrumentation and data collection for soil moisture, soil properties, depth to shallow groundwater was conducted along these hydrological positions for both wetland systems. In addition, there was data mining from other sources. Following the field-based analysis at a wetland scale in the inland valley, the spatial and temporal variability in soil moisture increased significantly (p In the Kilombero floodplain, Hydrus-1D model was successfully calibrated (R2 = 0.54–0.92, RMSE = 0.02–0.11 cm3/cm3) using measured soil moisture content. Satisfying statistical measures (R2 = 0.36–0.89, RMSE = 0.03–0.13 cm3/cm3) were obtained when calibrations for one plot were validated with measured soil moisture for another plot within the same hydrological zone, indicating the transferability of the calibrated Hydrus-1D. The hydrological regimes correlated with the hydrological positions in the floodplain. Soil moisture dynamics is controlled by overbank flow, precipitation, and groundwater control at the riparian and middle zone, while it is controlled by rainfall and lateral flow from mountains at the fringe 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. For the wetland-catchment scale hydrological modeling in the inland valley, good model performance was achieved from the calibration and validation of daily discharge (R2 and NSE > 0.7) for both model setups (ArcSWAT2012 and SWATgrid). The annual water balance indicates that 849.5 mm representing 65% of precipitation is lost via evapotranspiration. Surface runoff (77.9 mm) and lateral flow (86.5 mm) are the highest contributors to stream flow. Four land use management options were developed in addition to the current land use system, with different water resources conservation levels (Conservation, Slope conservation, Protection of the headwater catchment, and Exploitation). There is a strong relationship between the first three management options with decreasing surface runoff, annual discharge and water yield while the fourth option will increase annual discharge and total water yield. The future climate change in the inland valley was analyzed using climate scenarios RCP4.5 and 8.5 of six GCM-RCM models from the CORDEX-Africa project. Compared to the reference period of 1976-2005, a general increase in temperature of +0.9 0C to +1.9 0C over the period of 2021-2050 is projected by the model ensemble. A mixed change signal in annual precipitation (-30 to 43.9%) is projected among the six climatic models. However, on average, the models show an increase in annual precipitation of +7.4% and +21.8% under RCP4.5 and 8.5, respectively. The application of the climate model ensembles in SWAT showed future discharge change similar to the projected precipitation change. The six climate models showed uncertainty in the annual discharge change ranging from -44 to 149% although on average, the climate models project an increase of +16% and +29% under RCP4.5 and 8.5, respectively. Wet and dry seasons are expected to get wetter and drier, respectively in the future. Compared to land use management options, climate change will have a dominant impact on the water resources in inland valleys. Adoption of Conservation, Slope conservation and protection of the headwater catchment options will significantly reduce the impacts of climate change on the total water yield and surface runoff and increase evapotranspiration and water availability in the inland valley

Climate Smart Agriculture in Uganda

Population growth, rapid urbanization, and dietary changes are placing tremendous pressure on food systems, particularly in developing countries. Based on current income, population and consumption trends, the Food and Agriculture Organization of the United Nations (FAO) estimates that, by 2050, some 50 percent more food will be needed to satisfy the extra demand compared to 2013 (Alexandratos and Bruinsma, 2012). The challenges posed by rapid growth in food demand are intensified by the effects of climate change on agricultural systems, including crops, livestock, forestry and fisheries. Climate change effects will vary by region, country and location and will affect people differently depending on their vulnerability and capacity to adapt. Some areas are expected to become drier and more droughtprone, while others will witness more intense rains or altered rainfall patterns as well as mean temperature changes. In Uganda, climate projections based on the Global Climate Models (GCMs) used in the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change (IPCC) indicate the possibility of an increase in the country’s near-surface temperature in the order of +2°C in the next 50 years, and +2.5°C in the next 80 years using Representative Concentration Pathway (RCP) 4.5 scenarios (Zinyengere et al., 2016). They also predict a slight decrease in total annual rainfall in most of the country, with slightly wetter conditions over the west and north-west under both RCP 4.5 and RCP 8.5 scenarios. These events threaten food production and the livelihoods of food producers, particularly those with the weakest adaptation capacity who are too often located in areas exposed to the most severe changes. Moreover, for agricultural systems to sustainably contend with climate change, their contribution to greenhouse gas (GHG) emissions must also be addressed. Therefore, this added variability changes the conditions in which agriculture is practiced and requires context and site-specific strategies and responses

Effect of Mulching and Permanent Planting Basin Dimensions on Maize (Zea mays L.) Production in a Sub-Humid Climate

In sub-humid regions, declining maize (Zea mays L.) yield is majorly attributed to unreliable rainfall and high evapotranspiration demand during critical growth stages. However, there are limited farm technologies for conserving soil water and increasing water use efficiency (WUE) in rainfed production systems amidst a changing climate. This study aimed at assessing the performance of different climate smart agriculture (CSA) practices, such as mulching and permanent planting basins (PPB), on maize growth, yield, water use efficiency and soil moisture storage. Field experiments involving mulches of 2 cm (M_2 cm), 4 cm (M_4 cm) and 6 cm (M_6 cm) thickness, permanent planting basins of 20 cm (PPB_20 cm) and 30 cm (PPB_30 cm) depths and the control/or conventional treatments were conducted for three maize growing seasons in the sub-humid climate of Western Uganda. Results indicate that maize biomass significantly increased under the tested CSA practices in the study area. Use of permanent planting basins relatively increased maize grain yield (11–66%) and water use efficiency (33–94%) compared to the conventional practice. Additionally, plots treated with mulch achieved an increase in grain yield (18–65%) and WUE (28–85%) relative to the control. Soil amendment with M_4 cm and M_6 cm significantly increased soil moisture storage compared to permanent planting basins and the conventional practice. Overall, the results highlight the positive impact of CSA practices on improving maize yield and water use efficiency in rainfed agriculture production systems which dominate the sub-humid regions

Impact of Climate and Land Use/Land Cover Change on the Water Resources of a Tropical Inland Valley Catchment in Uganda, East Africa

The impact of climate and land use/land cover (LULC) change continues to threaten water resources availability for the agriculturally used inland valley wetlands and their catchments in East Africa. This study assessed climate and LULC change impacts on the hydrological processes of a tropical headwater inland valley catchment in Uganda. The hydrological model Soil and Water Assessment Tool (SWAT) was applied to analyze climate and LULC change impacts on the hydrological processes. An ensemble of six regional climate models (RCMs) from the Coordinated Regional Downscaling Experiment for two Representative Concentration Pathways (RCPs), RCP4.5 and RCP8.5, were used for climate change assessment for historical (1976-2005) and future climate (2021-2050). Four LULC scenarios defined as exploitation, total conservation, slope conservation, and protection of headwater catchment were considered. The results indicate an increase in precipitation by 7.4% and 21.8% of the annual averages in the future under RCP4.5 and RCP8.5, respectively. Future wet conditions are more pronounced in the short rainy season than in the long rainy season. Flooding intensity is likely to increase during the rainy season with low flows more pronounced in the dry season. Increases in future annual averages of water yield (29.0% and 42.7% under RCP4.5 and RCP8.5, respectively) and surface runoff (37.6% and 51.8% under RCP4.5 and RCP8.5, respectively) relative to the historical simulations are projected. LULC and climate change individually will cause changes in the inland valley hydrological processes, but more pronounced changes are expected if the drivers are combined, although LULC changes will have a dominant influence. Adoption of total conservation, slope conservation and protection of headwater catchment LULC scenarios will significantly reduce climate change impacts on water resources in the inland valley. Thus, if sustainable climate-smart management practices are adopted, the availability of water resources for human consumption and agricultural production will increase

The Corona Pandemic’s Impact on the Food and Nutrition Security of Refugees in Northern Uganda

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Potential of Moisture Conservation Practices to Improve Soil Properties and Nutrient Status of Robusta Coffee Plant

Soil moisture conservation practices (SMCPs) have been adopted in Uganda to adapt to the effects of climate variability. However, limited information exists on how conservation measures influence the physico-chemical properties of soil and coffee leaf nutrient concentrations. Thus, we determined the effects of selected SMCPs on the soil physio-chemical properties and leaf nutrient concentrations in Robusta coffee in a randomized incomplete block design, replicated three times, in Kituza, Uganda. Soil samples were collected from 0 to 20 cm and 20 to 40 cm depths, and analyzed in the laboratory following standard procedures for selected physio-chemical properties. Coffee leaf samples were picked from each treatment (open sun coffee (COSS), coffee cover crop, Desmodium intortum (CCS), coffee mulch, Miscanthidium violoceum (CMS), and coffee A. coriaria (ACS)). Bulk density was significantly (p −3) and lowest under CCS (1.29 gcm−3), and it significantly (p < 0.001) increased with depth. The soil organic matter was higher than the optimum range of 1–3% at the 0–20 cm depth across different SMCPs, but within the optimum range at the 20–40 cm depth. Leaf nitrogen was significantly the highest under ACS (3.19%) and lowest under COSS (2.30%). Overall, the findings suggest that SMCPs improve the soil physio-chemical attributes and leaf nutrients for sustainable coffee productivity. However, ACS improved the leaf plant nutrition better compared to other SMCPs

Impacts of Climate Smart Agriculture Practices on Soil Water Conservation and Maize Productivity in Rainfed Cropping Systems of Uganda

With climate change, maize production is becoming more constrained by limited water availability especially in rainfed production systems. Climate Smart Agriculture (CSA) practices have potential to enhance water availability and water use efficiency in rainfed production systems, but their efficiencies have not been adequately investigated. The study evaluated the performance of permanent planting basins (PPB), mulching (M), and halfmoon pits (HM) on soil moisture storage, maize yield, and water use efficiency in a maize cropping system for the sub-humid areas of Uganda for three cropping seasons in Albert region. The control treatment consisted of bare soil as the existing conventional farming practice without any CSA practice. Maize growth parameters and soil moisture storage were monitored and evaluated in each cropping season and CSA treatment. The maize yield, water use efficiency, and evapotranspiration (ET), were determined in each CSA treatment. Results showed that CSA practices significantly increased (P < 0.05) total soil water storage (1–12%) than the control treatment. It was also noted that; the use of M, PPB, and HM increased the water use efficiency by 9 – 68% and 8 – 66% of grain yield compared to the control in the three growing seasons. Our results indicate that even under unreliable and limited precipitation in sub-humid regions, the studied CSA practices indicate a high possibility to increase maize productivity than conventional farming practices (control). These findings are critical as climate change continues to affect maize productivity in rainfed farming systems where there limited supplemental water alternative sources for smallholder farmers. The adoption of CSA practices will enhance the resilience of maize production in sub-humid regions

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

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; R2 = 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 (R2 = 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

Land Cover and Soil Properties Influence on Forage Quantity in a Semiarid Region in East Africa

Soil properties contribute to the widely recognised resilience of semiarid areas. However, limited attention has been given in providing a scientific basis of how semiarid soil properties in the various land covers occur and how they influence forage quantity. This study investigated the influence of different soil properties and land cover types on herbaceous biomass quantity in the Karamoja subregion of Uganda. A completely randomized design in three land cover types (thickets and shrublands, woodlands, and savannah grasslands) was implemented. In each vegetation type, 50 × 40 m plots were demarcated with nested plots to facilitate clipping of the herbaceous layer. Composite soil samples at two depths (0–15 cm, 15–30 cm) were obtained from each plot. The results showed that soil properties varied across land cover types. Soil pH ranged between 6.9 and 8.1 and SOM, N, P, and K were generally low in all land cover types. Soil hydraulic properties revealed the existence of rapid to very rapid permeability in thickets/shrublands, grasslands, and woodlands. Percent change in soil properties (0–15 cm to 15–30 cm) was highest in P, Ca, Mg, Na, and SOM. In the grasslands, P positively (p≤0.01) influenced herbaceous biomass, whereas pH, K, Na, % sand, and % clay, N, and SOM had a negative relationship with herbaceous biomass (p≤0.05). Herbaceous biomass in the thickets/shrublands was negatively influenced by P, Ca, and Mg and % clay and positively by N and % silt (p≤0.05). Only N and SOM were significant determinants of herbaceous biomass in the woodlands (p≤0.05). The low level of soil nutrients observed in this study reveals the fragility of semiarid soils, indicating the need for sustainable landscape management