soil moisture graph Flashcards
soil moisture deficit
The degree to which soil moisture falls below field capacity. In temperate areas like the UK during late winter and early spring, soil moisture deficit is usually very low, due to high levels of antecedent rainfall and limited evapotranspiration in previous months
soil moisture recharge
Occurs in autumn when precipitation exceeds potential evapotranspiration - there is some refilling of water in the dried up pores of the soil
soil moisture surplus
Is the period when soil is saturated and water cannot enter and so flows over the surface - typically first few months of calendar year
soil moisture utilisation
Process operating in summer by which water is drawn to the surface through capillary action
field capacity
Is when soil holds all the water it can without any outputs
how is infiltration affected during rainfall
as the length of the rainfall event increases, the rate of infiltration decreases and surface runoff increases. This is because there is an increasing amount of water in the soil, reducing the potential for infiltration.
I.e. infiltration will decrease as surface runoff increases as soil is saturated
how does antecedent soil moisture affect infiltration
If the soil is relatively dry there is more potential for infiltration to occur. However, initially there is little difference between wet or dry soils as there may still be pore spaces near the surface that contain air as water has moved downwards. Once these pore spaces are filled infiltration decreases.
how does soil porosity affect infiltration
As soil porosity increases, infiltration increases and surface runoff decreases. There is a positive relationship between porosity and infiltration and an inverse relationship between infiltration and surface runoff. This is due to the large size of the pore spaces - large pore spaces allow more water to infiltrate than small pore spaces
how does vegetation cover influence infiltration
Vegetation has a major impact on infiltration and surface runoff. Infiltration is rapid over bare earth and lower under forest cover. It is high over bare earth initially, but declines rapidly as the pore spaces in the upper soil layer fill up with water. Under vegetated surfaces infiltration decreases more slowly as there is a lower amount of water reaching the ground and the reduced speed with which water reaches the ground.
how does raindrop size influence infiltration
As raindrop size increases, infiltration decreases - mainly due to the size of the raindrop exceeding the pore spaces they are entering. As infiltration decreases, surface runoff increases.
how does slope angle affect infiltration
As slope angle increases, so does the influence of gradient, infiltration rates decrease and surface runoff increases. This is because gradient affects the amount of time water remains on a slope - remains longer on lower angle slopes, so more potential for infiltration
water balance equation
precipitation = discharge + evapotranspiration +/- storage in soil and rocks
P = O +E +/- S
