ATMS 120 1st Edition Lecture 15 Outline of Last Lecture I Hurricane structure II Ingredients conducive for development III Destructive forces IV Storm surge V Inland flooding VI High winds Outline of Current Lecture I Drought worldwide II Drought III Heat waves IV 1995 Chicago heat wave V US drought monitor VI Causes of drought in central US VII Major drought in the US in the last 100 years Current Lecture I Drought is the longest lasting and deadliest weather related disaster on the planet No other weather phenomenon has shaped human existence more than drought Desertification the extreme deterioration of land in arid and dry sub humid areas due to loss of vegetation and soil moisture In the Sahel region just south of the Sahara Desert rainfall per year began to dip lower than average for several years in a row starting in 1970 These multiple years of below average rainfall is a result of the expanding Sahara Desert Lake Chad has since disappeared as a result of desertification and overuse irrigation II Drought is the 1 killer worldwide It is the largest weather related disaster It is the longest lasting weather related disaster There are four different types of drought Meteorological long time period of below normal precipitation These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Hydrological deficit in ground water or stream river flow Agricultural reduction in top soil moisture 1 st type of drought to set in Socioeconomic water supply reduced for human consumption sends us into mass migration famine and war III On warm days as relative humidity increases so does the heat index The heat index is the apparent temperature that we perceive Our bodies sweat to cool off The higher the RH the more difficult it is to evaporate water into the air Sweating does not happen as efficiently the higher the relative humidity Humans are much more sensitive to heat than to cold our body temperatures can get as low as about 40 degrees but only as high as about 106 before permanent damage starts to occur Assumptions when measuring heat index Pressure 1013 25 mb Measured in the shade 5 mph wind IV The presence of a large city can affect the air temperature because the materials used to construct these large cities absorb heat very well During the heat wave of Chicago in 1995 between 700 1000 people lost their lives the majority of them being poor or elderly people The major problem was that this heat island kept temperatures too high at night People living in low income neighborhoods lock their doors and windows at night for safety They are also typically not able to afford air conditioning or even a box fan These people basically baked in their homes V The Palmer Drought Severity Index PDSI is used based on groundwater supply balance The balance is between supply from precipitation and stored water and the depletion from temperature dependent evaporation recharge of sub surface water and runoff The key feature of the drought indices is that they are region specific and cumulative Precipitation is monitored with Doppler radar and a rain gauge network called a tipping bucket In the western US drought would typically begin in the winter because they get their water from snow in the mountains to the east of them In the eastern US drought would typically begin in the spring because we rely on our spring rainfalls VI The key idea is persistent departures from normal large scale weather patterns When a jet stream puts central Illinois under a semi permanent ridge a positive feedback cycle occurs Ridge creates a high pressure system at the surface leads to sinking motion which promotes clear skies sun heats up the surface dries out the ground which causes no moisture to form clouds heating at the surface builds the ridge aloft VII The 1988 drought was the 3rd most costly natural disaster behind Hurricanes Katrina 1 and Sandy 2 It was called the One Year Drought It hit the breadbasket and cut corn production in half It was this drought that burned down Yellowstone National Park During the drought of the 50 s Texas was the hardest state that was hit 244 out of 254 counties in Texas were federal disaster areas Groundwater levels dropped 50 100 feet and remain that way today There was a catastrophic loss in cattle graze land Fields in Texas are now circular because of the irrigation systems they use The Dust Bowl was the worst natural disaster in US history It hit during the Great Depression The Dust Bowl was due to both weather conditions and human influences Record heat and below normal rainfall for a decade combined with very poor land management techniques contributed to the Dust Bowl Dust storms are also referred to as black blizzards