Impact of two different types of El Niño events on runoff over the conterminous United States
The responses of river runoff to shifts of large-scale climatic patterns are of increasing concerns to water resource planners and managers for long-term climate change adaptation. El Niño, as one of the most dominant modes of climate variability, is closely linked to hydrologic extremes such as flo...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-01-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | http://www.hydrol-earth-syst-sci.net/20/27/2016/hess-20-27-2016.pdf |
| Summary: | The responses of river runoff to shifts of large-scale climatic
patterns are of increasing concerns to water resource planners and managers
for long-term climate change adaptation. El Niño, as one of the most
dominant modes of climate variability, is closely linked to hydrologic
extremes such as floods and droughts that cause great loss of lives and
properties. However, the different impacts of the two types of El Niño, i.e., central Pacific (CP-) and eastern Pacific (EP-)El Niño, on runoff
across the conterminous US (CONUS) are not well understood. This study
characterizes the impacts of the CP- and EP-El Niño on seasonal and
annual runoff using observed streamflow data from 658 reference gaging
stations and the NCAR-CCSM4 model. We found that surface runoff responds
similarly to the two types of El Niño events in southeastern, central,
southern, and western coastal regions, but differently in northeast (NE),
Pacific northwest (PNW) and west north central (WNC) climatic zones.
Specifically, EP-El Niño events tend to bring above-average runoff in
NE, WNC, and PNW throughout the year while CP-El Niño events cause
below-than normal runoff in the three regions. Similar findings were also
found by analyzing NCAR-CCSM4 model outputs that captured both the CP- and
EP-El Niño events, representing the best data set among CMIP5 models. The
CCSM4 model simulates lower runoff values during CP-El Niño years than
those in EP-El Niño over all of the three climatic regions (NE, PNW, and
WNC) during 1950–1999. In the future (2050–2099), for both types of El
Niño years, runoff is projected to increase over the NE and PNW regions,
mainly due to increased precipitation (<Emphasis Type="Italic">P</Emphasis>). In contrast, the increase of
future evapotranspiration (ET) exceeds that of future <Emphasis Type="Italic">P</Emphasis>, leading to a projected
decrease in runoff over the WNC region. In addition, model analysis
indicates that all of the three regions (NE, PNW, and WNC) are projected to
have lower runoff in CP-El Niño years than in EP-El Niño years. Our
study suggests that the US water resources may be distributed more
unevenly in space and time with more frequent and intense flood and drought
events. The findings from this study have important implications to water
resource management at regional scales. Information generated from this
study may help water resource planners to anticipate the influence of two
different types of El Niño events on droughts and floods across the
CONUS. |
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| ISSN: | 1027-5606 1607-7938 |