Contrasts in this context probably refer to changes/differences in the water cycle. Probably start by defining the hydrological cycle, state the physical factors like geology, climate, soil, relief, vegetation. Then explain each of them eg. geology and permeability affects infiltration rates. Vegetation can increase evapotranspiration- transfer of water from stores to the atmosphere, climate can change the levels of precipitation etc. Maybe link to climate change for wider links eg. extreme weather, hot temp- increased evaporation, decreased water table. Hope that helps, then again im not sure what the figure is showing so idk exactly what to say. Good luck!