An analytical equation is given for the dependence of the parameters of the reclamation regime of the catchment area on the volume of runoff and the width of the range of self-regulation of the ecosystem at a level of 80% of the maximum productivity of the autotrophic link of the ecosystem. Analytical formula is given for determining the parameters of the reclamation regime of the catchment ecosystems. It is noted that ecosystem water use (management of the use of water resources by the ecosystem) makes it possible to predict the direction of development of the river basin ecosystems and manage (minimize the risks) the supply of water for irrigation of agricultural fields in the context of climate changes. The proposed approach allows not only to improve on water supply of agriculture, but also to optimize carbon absorption by the catchment ecosystem, including agricultural land.