| With the rapid increase of population,the demand pressure of human survival and development on water and land resources continues to intensify.Water security,a key policy objective for sustainable development,is under pressure from land use and climate change,especially in arid and semi-arid regions.Land use change alters surface runoff,which affects hydrological processes and water consumption across the basin,and climate change alters precipitation and temperature patterns,which alters evapotranspiration and water supply.The Lake Victoria Basin in East Africa is a typical inland great lake region.With the impact of climate change and human activities,the Basin has faced a series of problems such as dense population,scarcity of water resources,food shortage,and deterioration of the ecological environment in recent years.Therefore,in the context of climate change,how to achieve a reasonable allocation of water and soil resources in the basin under the premise of promoting water balance,food security and ecological protection in the basin is the focus of the research.Based on the summary and analysis of domestic and international research progress,a multi-objective optimization model(MOP)under climate change is constructed in this paper.Finally,the land use change simulation model(PLUS)is introduced to realize the spatial layout simulation of the land use optimization results,and the differences of land use changes in each sub-basin and the achievement of the target are observed.The main conclusions were:(1)The Lake Victoria Basin as a whole is facing severe water resources pressure.The spatial distribution of precipitation in the basin is uneven.Most of the precipitation falls on the northern upland of the basin,while the central and southeastern regions receive relatively little rainfall.Evapotranspiration,as an important part of the water balance in the basin,accounts for about 87% of the rainfall in the basin.The total water consumption,including domestic water consumption,industrial water consumption,and evapotranspiration water consumption,showed a relatively consistent spatial distribution with precipitation.The calculation results of the water stress index show that in 2017,only 27% of the area in the Lake Victoria Basin faced moderate water stress,60% of the area faced severe water resource stress,and 13% of the area faced extreme water stress.In terms of spatial distribution,the extreme water stress areas are mainly located in the southeast of the basin(Simiyu sub-basin),the central-eastern part of the basin,and central Rwanda(Sondu and Nyabarongo sub-basin).(2)With climate change and social and economic development,there are significant differences in precipitation and water consumption in each sub-basin.Under the future RCP6.0 scenario,the climate change in the basin is mainly manifested in a 1% increase in precipitation and a 0.62% increase in potential evapotranspiration.In the southwestern part of the basin(Ikimba,Rwagritugusa,Burigi,Akanyaru,Nyawarungu sub-basins)precipitation decreased,but potential evapotranspiration increased with climate change.In the socio-economic water consumption forecast,compared with 2017,the industrial water consumption and domestic water consumption in the basin will increase by about 39% and 56%respectively in 2030,and the changes in the total socio-economic water consumption in the southwestern part of the basin are significantly higher than the average level of the basin.Therefore,to optimize the management of water and land resources in a large-scale watershed,it is necessary to consider the differences in the characteristics of each sub-basin.(3)Based on a multi-objective optimization model,the land use allocation scheme is optimized under the background of water resource balance,grain production and ecological protection in the basin.After optimization,land use is mainly manifested in the reduction of rained cultivated land and the orderly development of irrigated cultivated land;considering ecological protection,forest land and grassland have been restored to varying degrees.Under the RCP6.0 concentration path,the water stress index of the optimized scheme eased by 0.52%compared with 2017,the biomass production increased by 0.22%,and the per capita grain production increased by nearly 8%.This program can play a positive role in coping with socio-economic development and climate change,and mitigate the negative impacts of rapid development.(4)Based on the coupling model of multi-objective planning and land use change simulation,there are differences in the direction of land use optimization in different regions of the watershed.The simulation results of land use spatial change mainly show that under the condition of coordinated development,the high consumption of rain-fed cultivated land in the southwestern regions(Burigi,Akanyaru,Kagera-rwanda,Nyawarungu,and Kagera-tanzania sub-basins)where water resources are scarce in the future should be minimized.For the area of water and land,focus on increasing the area of irrigated cultivated land in the northeast and southern regions of the river basins(Simiyu,Grumeti,Nyando,Yala,Mori,Mbalaget sub-basins)with rich water systems and water resources in the future to ensure the increase in regional grain production.In the south and northeastern part of the Lake Victoria Basin(Simiyu,Yala,Geita-bukoba,Nyando,Nzola,Sondu,Isanga sub-basins),that is,the sub-basins where the national parks and protected areas are located,mainly increase ecological land such as forest land to give full play to its ecological protection Function.(5)The basin as a whole is expected to achieve multi-objective comprehensive optimization.However,under the background of future global warming,in the west of Lake Victoria basin will still face the problem of increased water stress.The development of various water storage projects should be accelerated to make precipitation more localized for usable water resources. |
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