Learning objectives To understand the water balance To understand how the water balance can change in different environments

Remember the drainage basin system Remember the drainage basin system!! Can you remember the 3 outputs and the 1 input? The water balance, or water budget is the balance between these inputs and outputs River Runoff Outputs = river runoff and evapotranspiration Inputs = precipitation Transpiration Precipitation Evaporation

P = O + E +/- S The Water Balance Scientists want to know what happens to the water when it enters the drainage basin system. This helps to plan for future water supply and also to help control flooding. Precipitation = Total runoff (streamflow) + Evapotranspiration +/- Storage (soil or rock P = O + E +/- S

Precipitation = Total runoff (streamflow) + Evapotranspiration +/- Storage (soil or rock P = O + E +/- S 100% = + + 50% 30% 20%

The Water Budget Graph The water budget (water balance) can be represented by an equation and by a graph… The graph looks at how evaporation and precipitation levels affect soil moisture levels Soil moisture recharge Soil moisture utilisation Soil moisture surplus Soil moisture deficit

The Water Budget Graph Mean Precipitation (mm) J F M A M J J A S O N D When evaporation exceeds precipitation in the summer the soil water is utilized… … there is a soil moisture or water surplus. This water is now available to supply rivers By the second half of summer there is a soil moisture deficit Mean Evapotranspiration (mm) Mean Precipitation (mm) Precipitation increased and evapotranspiration falls in the autumn allowing soil moisture to be recharged once more 5 J F M A M J J A S O N D In the winter precipitation exceeds evaporation and soil moisture is recharged until… Soil moisture recharge Soil moisture utilisation Soil moisture deficit Soil moisture surplus

What if precipitation exceeds evaporation in the winter? What if GAME….. What if precipitation exceeds evaporation in the winter? What if evaporation exceeds precipitation in the summer?

TASK Use the table below to draw a water budget graph for England Colour code the graph like the one on the left and annotate it to show what’s happening. Mean Evapotranspiration (mm) Mean Precipitation (mm) J F M A M J J A S O N D Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Precipitation (mm) 110 107 102 96 91 84 83 89 95 111 119 104 Evapotranspiration 10 22 41 69 90 114 124 126 115 70 11 15 Finished early? Can you explain your graph to the person next to you? Or do a sketch and explain it without looking?

How many of the new words can you remember in 60 seconds?? 60 second challenge How many of the new words can you remember in 60 seconds??