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- Author or Editor: Robin T. Shealy x
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Abstract
Results from a prior investigation of crop-yield shifts produced by simulated summer rain increases were coupled with summer rainfall forecasts to assess the possible economic outcomes of using forecasts to select the level of rain change for a summer. Simulated rain increases tested ranged from 10% to 40%. values not scientifically established as possible from midwestern cloud seeding, but chosen to provide a wide range of conceivable changes. The yields of corn and soybeans, under these different levels of simulated rain increases and grown under various growing season conditions experienced during a five-year agricultural plot experiment, varied considerably. To test the value of using a forecast, a summer rain forecast (above, below, or new average) made on 1 June and with an accuracy of 60%, was used as a guide to select the amount of rain change to use in each of the five test years. Then, the distribution of the financial gain from crop yields obtained was computed. The use of the forecasts showed an expected gain in 85% of the annual cases studied. Use of this forecasting skill (and hence less than perfect choice of level of precipitation augmentation to use in a given year), produced a gain in revenue expected over the five-years test period of 1.6% of the crop value, a possible maximum gain of 3.8%, and a possible maximum low of 0.6%. Rain increase applied without use of summer rain predictions (and based on use of the added rain level found best for continuous use in all five years) provided a revenue gain of only 0.4%, considerably less than the value obtained with the forecasts. If perfect rain forecasts existed, the expected gain would be 4.5% of the crop value. Even with a rain-modification technology that could deliver 10%, 25%, or even 40% rain increases in any given summer, the agricultural value of rain augmentation in Illinois done over a series of years is relatively small, even when coupled with forecasts.
Abstract
Results from a prior investigation of crop-yield shifts produced by simulated summer rain increases were coupled with summer rainfall forecasts to assess the possible economic outcomes of using forecasts to select the level of rain change for a summer. Simulated rain increases tested ranged from 10% to 40%. values not scientifically established as possible from midwestern cloud seeding, but chosen to provide a wide range of conceivable changes. The yields of corn and soybeans, under these different levels of simulated rain increases and grown under various growing season conditions experienced during a five-year agricultural plot experiment, varied considerably. To test the value of using a forecast, a summer rain forecast (above, below, or new average) made on 1 June and with an accuracy of 60%, was used as a guide to select the amount of rain change to use in each of the five test years. Then, the distribution of the financial gain from crop yields obtained was computed. The use of the forecasts showed an expected gain in 85% of the annual cases studied. Use of this forecasting skill (and hence less than perfect choice of level of precipitation augmentation to use in a given year), produced a gain in revenue expected over the five-years test period of 1.6% of the crop value, a possible maximum gain of 3.8%, and a possible maximum low of 0.6%. Rain increase applied without use of summer rain predictions (and based on use of the added rain level found best for continuous use in all five years) provided a revenue gain of only 0.4%, considerably less than the value obtained with the forecasts. If perfect rain forecasts existed, the expected gain would be 4.5% of the crop value. Even with a rain-modification technology that could deliver 10%, 25%, or even 40% rain increases in any given summer, the agricultural value of rain augmentation in Illinois done over a series of years is relatively small, even when coupled with forecasts.
Abstract
Long-term (1921–90) daily precipitation data from 242 stations were used to identify heavy multiday precipitation events (exceeding the threshold for a 1-yr recurrence interval) that were found to be closely related to flood events. The number of events were aggregated over 5-yr (pentad) periods and compared with total pentad precipitation. Although a strong positive correlation was found, this was due entirely to the event contributions to the total precipitation. When event precipitation was subtracted from total precipitation, no statistically significant correlation was found. The frequency distribution of precipitation totals in nonevent weeks was also found to be similar in years with few or no events compared to years with several events. These findings suggest that the occurrence of these events is not strongly linked to longer-term persistent climate anomalies. These relatively few events make an important contribution to long-term precipitation variability, accounting for about half of the interpentadal variability.
To provide information for determining hydrologic impacts from the results of GCMs, a study of spatial precipitation variability during heavy events was undertaken. For each event at each station, grid-average precipitation was calculated for 2° latitude × 2.5° longitude, and 4° latitude × 5° longitude grid cells. The ratio of grid average to heavy-event precipitation totals was determined. These relationships could be used to assess the probability of flood-producing, localized precipitation extremes from GCM grid-average precipitation.
Abstract
Long-term (1921–90) daily precipitation data from 242 stations were used to identify heavy multiday precipitation events (exceeding the threshold for a 1-yr recurrence interval) that were found to be closely related to flood events. The number of events were aggregated over 5-yr (pentad) periods and compared with total pentad precipitation. Although a strong positive correlation was found, this was due entirely to the event contributions to the total precipitation. When event precipitation was subtracted from total precipitation, no statistically significant correlation was found. The frequency distribution of precipitation totals in nonevent weeks was also found to be similar in years with few or no events compared to years with several events. These findings suggest that the occurrence of these events is not strongly linked to longer-term persistent climate anomalies. These relatively few events make an important contribution to long-term precipitation variability, accounting for about half of the interpentadal variability.
To provide information for determining hydrologic impacts from the results of GCMs, a study of spatial precipitation variability during heavy events was undertaken. For each event at each station, grid-average precipitation was calculated for 2° latitude × 2.5° longitude, and 4° latitude × 5° longitude grid cells. The ratio of grid average to heavy-event precipitation totals was determined. These relationships could be used to assess the probability of flood-producing, localized precipitation extremes from GCM grid-average precipitation.
Abstract
Analysis of precipitation events in the St. Louis aera, based on pre-event low-level wind flow, was pursued to ascertain the presence of urban effects on fall, winter, and spring precipitation. Data from a circular, dense, raingage network were used to define quadrant (NW, NE, SE, SW) average precipitation. Winds before each event (443 events in 1971–75) were used to define the urban plume and identify which quadrant was “downwind” of the city. Results for fall revealed a 17% increase in precipitation downwind of St. Louis and a 13% increase in events with their peak rainfall occurring downwind, both outcomes were statistically significant at the 1% level. The downwind enhancement was greatest when pre-event winds were from the SE, and when average precipitation in the quadrant with the maximum value was either light (<5.1 mm) or quite heavy (>17.9 mm). The fall results agree well with earlier findings for summer rainfall that revealed a 25% increase due to enhancement in isolated airmass showers and during heavier, well-organized convective system Winter precipitation indicated little precipitation change downwind of St. Louis. However, when SW pre-event winds existed (a flow often associated with conviction), there was a statistically significant downwind increase in winter precipitation; but when pre-event winds were from SE or NW (flows frequently associated with stratiform precipitation), downwind decreases occurred. The number of spring precipitation conditions that maximized downwind of St. Louis was significantly greater than expected by chance particularly in light (<5.1 mm) events, but the total spring rainfall downwind increased only 4%. There was no suggestion of decreased precipitation in spring or fall. The urban influences to enhance precipitation appeared to be related to precipitation conditions with convective processes, and urban influences in more stratiform precipitation situations were negligible.
Abstract
Analysis of precipitation events in the St. Louis aera, based on pre-event low-level wind flow, was pursued to ascertain the presence of urban effects on fall, winter, and spring precipitation. Data from a circular, dense, raingage network were used to define quadrant (NW, NE, SE, SW) average precipitation. Winds before each event (443 events in 1971–75) were used to define the urban plume and identify which quadrant was “downwind” of the city. Results for fall revealed a 17% increase in precipitation downwind of St. Louis and a 13% increase in events with their peak rainfall occurring downwind, both outcomes were statistically significant at the 1% level. The downwind enhancement was greatest when pre-event winds were from the SE, and when average precipitation in the quadrant with the maximum value was either light (<5.1 mm) or quite heavy (>17.9 mm). The fall results agree well with earlier findings for summer rainfall that revealed a 25% increase due to enhancement in isolated airmass showers and during heavier, well-organized convective system Winter precipitation indicated little precipitation change downwind of St. Louis. However, when SW pre-event winds existed (a flow often associated with conviction), there was a statistically significant downwind increase in winter precipitation; but when pre-event winds were from SE or NW (flows frequently associated with stratiform precipitation), downwind decreases occurred. The number of spring precipitation conditions that maximized downwind of St. Louis was significantly greater than expected by chance particularly in light (<5.1 mm) events, but the total spring rainfall downwind increased only 4%. There was no suggestion of decreased precipitation in spring or fall. The urban influences to enhance precipitation appeared to be related to precipitation conditions with convective processes, and urban influences in more stratiform precipitation situations were negligible.
