Hydrologic Forecasts

scientific predictions (of varying amounts of time in advance) of the development of a process occurring in a river, lake, or reservoir.

According to the character of the elements of the regimen being forecast, hydrologic forecasts are divided into water forecasts and ice forecasts. Water forecasts predict the volume of seasonal and flood runoff, maximum discharges of water and high-water or flood levels, average water discharges for various calendar periods, and the time of the maximum high-water level. Ice forecasts predict the times of breakup and freezing over of rivers, lakes, and reservoirs and the thickness of ice. Hydrologic forecasts may be short-range—for a period of up to 15 days—and long-range—for a period of 15 days to several months in advance. In terms of their purpose, distinctions are drawn between forecasts for hydroelectric power (inflow of water into the reservoirs of hydroelectric stations), for water transportation (forecasts of the water level on navigable rivers), and for irrigation (fore-casts of river runoff during the growing period). Hydrologic forecasting is one of the principal divisions of applied hydrology.