Water reserves are considered as renewable resources and the process of renewal is due to the water cycle in nature. However, the amount of water that emerges in this way on the surface of the earth or in any given geographical area is fixed, regardless of the changes between the years. In other words, the amount of renewable water that the earth's surface receives now and annually is equal to the water that it may have received thousands of years ago since the dawn of human civilization. This is while the spatial and temporal distribution of the amount of renewable water is completely variable and is not commensurate with the distribution of population and water needs of human societies. Obviously, the most accurate rainfall measurements are provided using traditional methods such as climatological stations, ground synoptics and rain gauges, but the accuracy of using this method in a dependent catchment Due to the spatial distribution of the stations and the sensitivity of its trustees in the maintenance of the stations, the realization of this important issue requires a lot of money and time. Accordingly, and since remote sensing is able to provide continuous, homogeneous and near-real-time information on the location and time in a particular area, even in inaccessible areas. There are several factors involved in evapotranspiration, the degree of effect of each of which depends on other factors, which makes it difficult to accurately estimate evapotranspiration. Some of these factors are air temperature, relative humidity, atmospheric pressure, amount of water-soluble substances, altitude and longitude. Thus it is impossible to use traditional methods and to directly calculate evapotranspiration without any degree of accuracy over a wide range. When the amount of rainfall in a catchment is more than the soil infiltration capacity, part of the rainwater flows as runoff on the surface of the catchment. The amount of runoff in a catchment depends on several factors including soil characteristics, catchment concentration time, geological conditions, climate and climate, slope and direction of slope, land use and drainage density. Various devices such as lysimeter and TDR device can be used to estimate the penetration rate directly; However, it is obvious that using these devices to estimate the infiltration rate in a large catchment area is very time consuming due to changes in the soil type of the catchment. Therefore, this component is calculated through methods, equations and relationships resulting from some hypotheses in hydrology. It is obvious that the accuracy of ground stations is much higher than satellite data, but in large basins due to the high cost of construction and maintenance of these stations and also the time consuming use of it. This study was conducted in the location of Tajan catchment area, which seems to be the ground stations located in it, both in terms of number and in terms of health due to the prosperity of agriculture and the location of Sari city with the majority of farmers in the region compared to other basins.