Final answer:
Diurnal slope flows are caused by temperature differences between the valley and surrounding areas, influenced by the local topography and microclimatic effects.
Step-by-step explanation:
Diurnal slope flows are ultimately caused by temperature differences between the valley and the surrounding areas. During the day, sunlight heats the slopes of the valley causing air to rise, and at night, the ground cools and the air descends into the valley. This vertical movement of air is due to the density differences that result from the heating and cooling of the air, hence the temperature differences.
These temperature variances are more pronounced in areas with varied topography, especially in hilly or mountainous regions. Notably, the local landscape has significant microclimatic effects and further influences soil development and evaporation rates.