Isotope measurements indicate transpiration is the larger component of evapotranspiration. Water flows out of wetlands by evapotranspiration, surface runoff, and subsurface water outflow. The difference between potential evapotranspiration and precipitation is used in irrigation scheduling. Coldest regions have not much evapotranspiration nor precipitation, hence polar deserts. The water table may vary due to seasonal changes such as precipitation and evapotranspiration. Hypobaric conditions can affect net photosynthesis and evapotranspiration rates. Especially in warm and dry climates the effects of evapotranspiration and precipitation are significant. As a consequence of reduced evapotranspiration, precipitation is also reduced. Similarly, as annual temperatures rise, grassland carbon stocks decrease due to increased evapotranspiration. Crop coefficients are properties of plants used in predicting evapotranspiration (ET). Soil moisture is almost always high because of lower evapotranspiration due to the cool climate. They act by regulating temperature extremes, increasing soil nutrients, and reducing evapotranspiration, among others. There are three general approaches to estimate evapotranspiration indirectly. The semi-arid classification is due to the city's high evapotranspiration. A third methodology to estimate the actual evapotranspiration is the use of the energy balance.