Global Warming Impacts on Hydrologic Extremes

• Author / Creator

  Gizaw, Mesgana Seyoum

• Climate change could significantly alter precipitation and water availability in different parts of the world. Moreover, during the course of the 21st century, climate change impact can potentially enhance the severity and frequency of extreme precipitation and also increase prolonged drought periods. This research focuses on the potential impact of climate change on extreme precipitation, floods and droughts in some selected study areas in North America and Africa. For the United States (US) and southern Canada, analysis of trends in Convective Available Potential Energy (CAPE) data and extreme precipitation indices for single or multiple storm events show an increasing trend over much of the eastern US and some parts of the Canadian prairies, e.g. southern Alberta, in the summer of 1979-2013. Statistically significant increasing trends in temperature and surface specific humidity is likely a major contributing factor to increasing trends in extreme precipitation events observed over these regions. Next, changes in extreme precipitation events in Oldman, Bow and Red Deer River Basins of southern Alberta, Canada, were also assessed using six extreme climate indices for the rainy May-August (MJJA) season, using dynamically downscaled SRES A2 and A1B climate scenarios of four Coupled Model Intercomparison Project phase 3 (CMIP3) Global Climate Models (GCMs). The results suggest that in the 2050s (2041-2070) and 2080s (2071-2100), southern Alberta will be expected to experience more frequent and severe intensive storm events in the MJJA season that could potentially increase the risk of future flooding. Regional Flood Frequency Analysis (RFFA) model based on the Support Vector Regression (SVR) was developed to estimate regional flood quantiles for two sites located in southeastern British Columbia (BC) and southern Ontario (ON), Canada. Based on historical predictors, SVR-RFFA satisfactorily estimated flood quantiles of 10, 25, 50 and 100 year return periods. Flood quantiles estimated by SVR-RFFA for 2041-2100 based on RCP4.5 and RCP8.5 climate scenarios project flood quantiles to increase by about 7% in southeastern BC and 29% in southern ON. Next, the possible impact of climate change on droughts in sub-Saharan Africa (SSAF) was analyzed using the Palmer Drought Severity Index (PDSI) for 1971-2000 and RCP4.5 and RCP8.5 climate projections of the 2050s and 2080s. The results show that most areas in South Africa (SA) and West Africa (WA) will shift to a drier climate in the 2050s and 2080s while some areas in Greater Horn of Africa (GHA) could be relatively wetter in this period. In contrast, very little change is projected in the drought severity of Central Africa (CA). More frequent El Niño episodes in 21st century could also increase the drought prone regions of WA, SA and GHA while CA still remains virtually unaffected. These results suggest that SSAF will experience a drier climate in the 2050s and 2080s with an increase in drought prone areas in the four corners of the sub-continent. The potential impact of climate change on water availability of parts of GHA was simulated by the Hydrologic Simulation Program-FORTRAN (HSPF) hydrologic model to predcit changes in the streamflow of four major river basins in Ethiopia: Awash, Baro, Genale and Tekeze. The calibrated and validated HSPF model was forced with bias corrected daily climate data from 10 CMIP5 GCMs for the 1971-2000 control period and the RCP4.5 and RCP8.5 climate projections of 2050s and 2080s. The results suggest that the mean annual streamflow of Awash, Baro and Tekeze rivers is projected to increase by about 3% (6%) whereas for Genale river about 18% (33%) increase in streamflow is projected for the 2050s (2080s). Despite the increase in annual streamflow, the mean summer streamflow is projected to decrease for most river basins. However, such a decrease in summer streamflow was compensated with a significant increase in the autumn streamflow. The results from this research suggest that climate change could significantly increase the frequency and intensity of hydrologic extremes such as severe precipitation and droughts which can also affect the streamflow of river basins in different parts of the world.

• Subjects / Keywords

  • Droughts
  • Hydrologic extremes
  • Global warming
  • Climate change
  • Floods
  • Extreme precipitation

• Graduation date

  Spring 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3GT5FT2G

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.