Changes in heat, water and seasonal timing affect where species can survive. Some cannot move or adapt quickly enough.
Warming increases the demand for evaporation. At higher temperatures, more water vapour can be present at saturation, helping intensify heavy rainfall where moisture is available. Elsewhere, greater evaporation and reduced or unreliable rain worsen drought. A stronger global water cycle can therefore bring both wetter and drier conditions in different places.
Each species needs suitable conditions to survive and reproduce. Warming can shift those conditions towards the poles or higher ground; changing rainfall alters water supply. Organisms may be unable to follow. Roads and broken-up habitats can block movement, while a mountaintop leaves no higher ground to reach.
Seasonal timing can fall out of step. Flowers, insects and breeding birds may respond to warming at different rates. A species can then miss a food source when it most needs it. Effects spread to predators, pollination and other relationships in the ecosystem.
Drought reduces plant growth, dries soil and stresses animals. Hot, dry weather favours wildfire where fuel and an ignition source are present. Too much rain can waterlog or erode soil, flood habitats and trigger slope failure. Some species in colder regions may initially benefit from longer growing seasons, but water, nutrients and heat extremes still limit growth.
Step by step
Conditions change
Temperature, rainfall and extremes change the supply of heat and water.
Species respond
Suitable habitats and seasonal timings shift, but movement and adaptation have limits.
Relationships change
Food, breeding and pollination can fall out of step, affecting other species.
Worked example: Why rainfall totals are not enough
Two years could have similar total rainfall, yet one receives long dry gaps interrupted by intense downpours. Plants may face water stress between storms while rapid runoff and erosion limit useful soil-water storage during storms. Distribution and intensity matter alongside the annual total.
Watch out for this
Every species can simply move towards the poles as temperatures rise.
Dispersal ability, habitat barriers, available land and the speed of change can prevent movement. Ecosystem partners may not shift together.
Check your understanding
Why can equal annual rainfall totals produce different ecosystem impacts?
- Annual totals contain no useful information at all.
- Plants respond only to the year-end sum.
- Timing and intensity change water availability, runoff and stress.