Seasonal variation in sunlight hours significantly affects the hydrological cycle in a drainage basin. The amount of sunlight received influences several key processes. During seasons with longer daylight hours, typically spring and summer, increased sunlight leads to higher temperatures, which enhance evaporation from water bodies and soil, as well as transpiration from plants. This increase in evapotranspiration can lead to a reduction in soil moisture and lower water levels in rivers and lakes, especially if not compensated by adequate rainfall. Conversely, in seasons with shorter daylight hours, like autumn and winter, reduced sunlight results in lower temperatures, decreasing evaporation and transpiration rates. This reduction can lead to higher soil moisture levels and increased water availability in rivers and streams, provided that precipitation is sufficient. Furthermore, seasonal changes in sunlight also affect plant growth and dormancy, which in turn influences transpiration rates. Thus, understanding the seasonal variations in sunlight is crucial for managing water resources and predicting hydrological responses in different seasons.

Extreme weather events such as heatwaves and droughts have profound impacts on the hydrological processes within a drainage basin. During heatwaves, high temperatures significantly increase evaporation rates from water bodies and soil, as well as transpiration rates from plants. This heightened evapotranspiration leads to a rapid depletion of soil moisture and reduction in river and stream flows, potentially resulting in drought conditions. Prolonged droughts exacerbate these effects, leading to severely reduced water availability for ecosystems and human use. Drought conditions can also harden the soil, reducing its infiltration capacity and increasing the likelihood of surface runoff during subsequent rainfall events, which can lead to soil erosion and flash flooding. Moreover, these extreme conditions can affect vegetation health, reducing plant cover and further impacting transpiration and soil protection. Understanding the impacts of such extreme weather events is critical for water resource management, especially in the context of climate change, which is expected to increase the frequency and intensity of such events.

Urbanisation significantly alters the hydrological response of a drainage basin, particularly in terms of temperature and precipitation. Urban areas, with their high concentration of buildings and paved surfaces, create 'urban heat islands' where temperatures are higher than surrounding rural areas. This increase in temperature can enhance evaporation rates, leading to a quicker return of moisture to the atmosphere, potentially influencing local precipitation patterns. Increased temperatures can also accelerate the transpiration process in any remaining vegetation. Furthermore, urban surfaces are largely impermeable, leading to reduced infiltration and increased surface runoff during precipitation events. This alteration results in more immediate and higher peak discharges in urban streams and rivers, often exacerbating flood risks. The combination of altered temperatures and reduced infiltration in urban areas thus significantly modifies the natural hydrological cycle of a drainage basin.

Different types of vegetation have distinct impacts on evapotranspiration rates within a drainage basin. The rate of evapotranspiration is influenced by the type of vegetation, its density, and the extent of its coverage. For instance, forests with large leaf areas and deep root systems have high transpiration rates, contributing significantly to the total evapotranspiration of a region. In contrast, grasslands or shrublands with less leaf area and shallower root systems will generally have lower transpiration rates. The type of vegetation also affects the interception of rainfall - dense canopies in forests intercept more rainfall, reducing direct runoff and increasing the moisture available for transpiration. Additionally, vegetation type influences the albedo effect, where different surfaces absorb and reflect varying amounts of solar radiation, thereby impacting local temperature and evaporation rates. Therefore, the type and distribution of vegetation within a drainage basin are key determinants in the overall evapotranspiration and, consequently, the water balance of the area.

Wind plays a significant role in evapotranspiration within a drainage basin. It influences evapotranspiration by affecting both the evaporation from soil and water surfaces and the transpiration from vegetation. Wind increases evapotranspiration rates by removing the air saturated with water vapour from around the leaves of plants and the surface of water bodies, thereby creating a gradient that enhances the movement of moisture from the surfaces to the atmosphere. This effect is particularly noticeable in windy areas, where constant air movement results in higher evapotranspiration rates. Additionally, wind can affect the temperature and humidity of an area, indirectly influencing the rate of evapotranspiration. For example, warm winds can raise temperatures, leading to increased evaporation and transpiration, while cool winds might have the opposite effect. Understanding the influence of wind is essential for accurately assessing the water balance within a drainage basin, particularly in areas where wind patterns are a significant climatic feature.