The impacts of climate change on rivers and streams in the world are severe and widespread, and we have already began to see changes. These changes will not only affect the way in which we manage our water resources, but will also drastically affect aquatic communities.
Increasing water temperature
One of the most obvious effects of climate change on hydrology is the increase of water temperatures. Stream water temperatures are rising in many places, including the Chesapeake Bay region, in which water temperatures have been monitored since the 1960s. The figure below shows that 79% of the river sites measured showed increases in water temperatures, with an average increase of 1.2 degrees Fahrenheit.
Changes in Stream Water Temperatures in the Chesapeake Bay Region, 1960 -2014- Source: epa.gov
This increase in stream temperatures will have drastic effects on stream ecosystems, especially fish. Many species of fish rely on cold waters to thrive, such as salmon and trout, and the amount of available habitat for these fish is expected to decrease drastically. This will force these fishes into smaller tributary streams higher up in the watershed, where stream temperatures are still at a comfortable level. The lower reach habitat may then be invaded by warm-water fishes such as bass, which are expected to increase their habitat range. Cold-water fish species that migrate between rivers and oceans (an anadromous life history), will also be affected by warm water in their migratory corridor and could die as a result.
Warm stream temperatures may result in massive fish die-offs, as was the case for migrating salmon in the Columbia River basin in the summer of 2015 – Source: nwcouncil.org
Less snowfall and earlier melt
Another major influence of climate change on hydrologic regimes is the changing of snowmelt processes. Snow is beginning to melt earlier and earlier, resulting in peak stream flows in snowmelt-dominated systems happening earlier each year. In the Western United States, peak stream flow is happening weeks earlier when analyzing the trend from 1948 to 2002 (below).
Trends in peak spring flow for streams in the western United States – (Stewart et al. 2005)
This change in snowmelt can have significant impacts on water resource management. Increased variability in spring melt times and changes in peak magnitude can disrupt traditional approaches to dealing with water resources. A loss of predictive capacity and a change from the normal flood regime can leave reservoir and power plant operators guessing. The climate change models also predict that more of the precipitation will fall as rain rather than snow. This will reduce summer flows and leave the western United States vulnerable if reservoir capacity is not adequate to store enough early spring melt water into the summer.
Increased variation in precipitation
The last impact of climate change on hydrologic regimes to be addressed in this blog is the effect of climate change on precipitation. Wet areas are becoming wetter and dry areas are becoming drier, and we have seen an increase in the variability of precipitation across the globe. This means more reliance on irrigation farming, more floods and more droughts. It can also lead to instability of ecological communities as those communities adapted to normal baseline conditions may become susceptible to invasion by non-native species. Changes to precipitation will also have major implications for food production across the planet, as we will need to plan and adapt to our changing planet, so that we can continue to feed ourselves in the future.
Floods and droughts are increasing as a result of climate change – Source: EPA.gov (note: web page may be removed soon)
However all hope is not lost. Recent advances in green infrastructure have provided evidence that with proper management, more water can infiltrate the soil in urban areas, and flood risk can be lowered. Riparian vegetation plantings along streams and rivers can help to lower stream water temperatures. Improved irrigation practices can help to reduce the amount of water used for farming. If we start working together soon, perhaps we can adapt to future changes.
Read more about what on earth is going on:
Barnett, T. P., Adam, J. C., & Lettenmaier, D. P. (2005). Potential impacts of a warming climate on water availability in snow-dominated regions. Nature, 438(7066), 303-309.
Eaton, J. G., & Scheller, R. M. (1996). Effects of climate warming on fish thermal habitat in streams of the United States. Limnology and oceanography, 41(5), 1109-1115.
Stewart, I. T., Cayan, D. R., & Dettinger, M. D. (2005). Changes toward earlier streamflow timing across western North America. Journal of climate, 18(8), 1136-1155.
Trenberth, K. E. (2011). Changes in precipitation with climate change. Climate Research, 47(1- 2), 123-138.