Thesis Defense: Assessments and Projections of Regional Hydro-climatic Variability over the Southern U.S.: Potential Teleconnections with El Niño/Southern Oscillation
25 April 2012, 11:00 AM
National Weather Center, Room 4140
120 David L. Boren Blvd.
University of Oklahoma
The objectives of this research are to (1) assess climate change in the Southern U.S. and to (2) study the hydro-climate interaction (e.g. drought) in basins of interest within Southern U.S., and to (3) examine the teleconnections between ENSO and regional precipitation/droughts patterns. Three regions of interest are selected for this comprehensive climate study: SCIPP region and ABRFC region and the Blue River Basin, all of which are located in the Southern U.S The results are listed in the sequence of the three objectives. (1) The results from climate change assessment show that the average temperature over the SCIPP region is anticipated to increase by 1.7 to 2.4 °C in the 21st century based on the different emission scenarios with a rate of change that is more pronounced during the second half of the century. Precipitation projections, conversely, do not exhibit a discernible upward or downward trend. Late 21st century exhibits slightly more precipitation than the early century, based on the A1B and B1 scenario, and fall and winter are projected to become wetter than the late 20th century as a whole. (2) A. Drought indices SPI and PDSI are used to assess and project the severity of droughts in the ABRFC region. Results show that widespread droughts mainly took place in the 1910s, 1930s, 1950s and 1960s in this region, which agrees well with the historical climate record. Both the SPI and PDSI project that more frequent and severe droughts will appear in the second part of the 21st century under both of the emissions scenarios. Future PDSI projects that more severe droughts will occur in the western parts of this basin under A1B scenario. These changes have profound implications for local water resources management as well as broader regional decision-making. B. Drought indices SPI, PDSI and SRI are used to assess and project the severity of droughts in the Blue River Basin. Results show that the three indices captured the historical droughts for the past 50 years and suggest that more severe droughts of wider extent are very likely to occur over the next 90 years, especially in the later part of the 21st century. This study found that SRI and SPI (PDSI) had a correlation coefficient of 0.81 (0.78) with a 2-month (no appreciable) lag time over the 1950-2099 time period across the basin. The study recommends that SRI is the most suitable indices for assessing future drought risks under an increasingly warmer climate, however, diversed drought indices from ecological and socioeconomic perspectives should be investigated and compared to provide a complete picture of drought and its potential impacts on the dynamically coupled nature-human system. (3) An ENSO index MEI, is used to investigate the teleconnections between ENSO and precipitation/drought pattern in the ABRFC region. The results show that MEI is highly correlated to precipitation/SPI of 12 month-scale with precipitation/SPI having 6 months of lag time from MEI variation. Over the 20th century, drought teleconnection to ENSO variability was most significant during the first quarter of the 20th century. The teleconnections were much poorer and diffused for the rest of the century. A nonlinear relationship is more likely to exist between MEI and SPI. Therefore, to make confident seasonal to annual climate forecast, more sophisticated mathematical tools and further investigation on the climate dynamics over the tropical Pacific are in great need. Finally, future efforts should involve the use of drought indices from ecological and socio-economic disciplines to achieve a comprehensive understanding of the Southern U.S. droughts. The investigation of the physical mechanisms behind tropical Pacific ENSO teleconnections over the Southern U.S. should also be conducted in the future work.