With the aid of the diagram, describe and explain the long-term varoations in river discharge in seasonally humid climate

In a seasonally humid climate, river discharge typically shows a distinct annual pattern. The diagram would likely illustrate high discharge during the wet season due to heavy rainfall and increased surface runoff, and significantly lower discharge during the dry season as rainfall decreases and evaporation increases. This creates a predictable cycle of high and low flow within each year.

Beyond the annual cycle, long-term variations refer to changes in this seasonal pattern over many years. The diagram would show that the magnitude of peak flows (wet season discharge) and trough flows (dry season discharge) can vary significantly from one year to the next, or show a gradual trend over decades. For example, some years might have exceptionally high peaks or prolonged low flows compared to the average.

These long-term variations are primarily driven by:

• Climate Change: Shifts in global weather patterns can alter the intensity, duration, and timing of wet and dry seasons. This might lead to more extreme rainfall events (higher peaks) or extended droughts (lower troughs) over time.
• Climatic Oscillations: Natural multi-year cycles like El Niño-Southern Oscillation (ENSO) can cause periods of prolonged drought or excessive rainfall, leading to multi-year periods of unusually low or high river discharge.
• Land Use Changes: Deforestation can reduce infiltration and increase rapid runoff, potentially leading to higher flood peaks and lower dry season flows. Urbanization increases impervious surfaces, accelerating runoff and reducing groundwater recharge, also impacting long-term discharge patterns.
• Water Abstraction and Dams: Human activities like building dams or abstracting large amounts of water for irrigation or consumption can significantly alter the natural flow regime, leading to reduced downstream discharge over the long term.