20 CADERNOS DE ANÁLISE E PROSPETIVA CULTIVAR N.º 31 AGOSTO 2024 – Sequeiro Managing water scarcity in rainfed agriculture requires an integrated approach MARIA HELENA SEMEDO Former Deputy Director-General of FAO Water scarcity in a changing climate: a challenge for rainfed agriculture Rainfed agriculture represents 80 percent of the total cultivated land and 96 percent of the cropland in sub-Saharan Africa. Due to highly variable rainfall, long dry seasons, recurrent droughts, dry spells, and floods, water management is especially critical for rainfed production – even more so with climate change. Climate change modifies the global water cycle, rainfall patterns, river runoff and groundwater recharge. Increased temperatures and CO2 levels increase evapotranspiration and reduce soil water, which in turn stresses plants in dry ecosystems, shortens crop growing periods and reduces yields. The Intergovernmental Panel on Climate Change (IPCC) reports that yield losses related to drought have occurred in 75 percent of harvested areas globally and increased in recent years. More frequent flooding has also impacted production through direct damage to crops, water-logging, and delays in planting. The IPCC projects that the contrast in annual mean precipitation between dry and wet regions, as well as between seasons, will increase globally with ‘wet getting wetter, dry getting drier’, with less but more intense rains, leading to both an increase in droughts and floods. More intense and/or longer droughts will expose rainfed crops to moisture stress reducing yields and quality. More intense rainfall, especially on degraded sloping lands, will result in more runoff with higher soil erosion and lower soil infiltration, reducing groundwater recharge. Constraints to improving rainfed system productivity differ greatly between regions. In arid areas, the absolute amount of water available is the major limiting factor. In semi-arid and dry sub-humid tropical regions, the biggest challenge is extreme rainfall variability in time and space. And in many areas – especially in drylands – poor soils with often poor capacity for water retention is also limiting. The high risk of water-related yield loss can adversely influence farmers’ investment decisions, including investments in labour, improved seed and fertilizers. Management options should therefore start by supporting farmers to adopt practices that reduce rainfall-induced risks. The solutions Managing water scarcity in rainfed systems should aim to combine practices that conserve water in soils and landscapes, promote the sustainable use and restoration of biodiversity (species, varieties and ecosystems) adapted and resilient to droughts and to projected precipitations, and consider alternatives to crops and/ or combining with livestock and forestry in agroforestry or silvopastoral systems. Soil moisture mapping for managing water scarcity: Water retained in the soil, known as soil moisture, is key to plant survival, to get nutrients and enables biological activity. It also controls soil albedo and heat fluxes through evaporation and plant transpiration. More water can be stored in soil and used more efficiently with soil management practices such as mulching, organic matter amendment and reduced tillage. These practices improve soil moisture content by 25-40 percent and are highly promoted among farmers under FAO’s Global Soil Doctors and Soil Recarbonization programmes. Despite its importance, soil moisture mapping and monitoring is not yet widely included in agricultural management tools. FAO has developed the WaPOR (Water Productivity through Open access of Remotely sensed derived data) portal to help countries monitor water productivity and inform management decisions in areas where improved practices are needed. WaPOR now includes a module on relative soil moisture in the root zone to identify biomass growth reduction and better plan interventions based on this information. Water harvesting techniques: Various water harvesting techniques, including innovative traditional techniques such as half-moons, bunds and zaï, developed by farmers in Africa and the Near East, allow to concentrate and facilitate infiltration of water in the soil. Rainwater harvesting in reservoirs
RkJQdWJsaXNoZXIy MTgxOTE4Nw==