Land Elevation Vs. Rainfall

Essay by PaperNerd ContributorCollege, Undergraduate February 2002

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For this research project, I plan to compare land elevation to total rainfall. I will illustrate the process of orographic precipitation and the effects it has on the land. Using data from web sites such as worldcimate.com, I will compare the information on the graphs in order to determine what elevations receive the most rainfall. Orographic precipitation is interesting to me because I always wondered how regions of higher elevation received more rain or snow. Also orographic precipitation can be very significant because it can be used to predict flooding during storms. People who live in mountain regions could be notified that during a storm they will receive a higher percent of rainfall when compared to lower elevation regions.

Based on my observations and knowledge learned in this class, I believe regions in higher elevation and on windward sides of mountains will receive more rainfall throughout the year when compared to regions with lower elevations.

Therefore cities on leeward sides of mountains will receive little rainfall due to the rain shadow effect. This is well illustrated in the image provided on page.

Orographic precipitation is caused by the lifting of moist air over a mountain barrier. Topographic barriers that block the path of horizontal air movements are likely to cause large masses of air to travel upslope. When a wind forces humid air to rise over a mountain or mountain range, the air cools at its dry lapse rate until its dew point is reached. At that point, condensation occurs and clouds begin to form. These clouds are the source of orographic precipitation on the windward side of the mountain. As the air is forced up to even higher elevations it continues to cool. Then once the rising air reaches the crest of the mountain range, it is no longer forced upward and begins to descend on the leeward side of the mountain. As soon as it begins to move down slope, adiabatic cooling is replaced by adiabatic warming and condensation/precipitation ceases. Consequently since there is no precipitation, a warming, drying wind can often blow down from the leeward side of the mountain range. Valleys and lowlands on the leeward side of mountain ranges receive much less precipitation and are said to be in the rain shadow of the mountains.

Orographic precipitation can occur at any latitude, any season, and at any time of the day. The only conditions are that there must be a topographic barrier and moist air must move over it. San Diego County is a great example of this rain shadow effect. Death Valley and other mountain-sheltered valleys of the western and southwestern United States are also rain shadow deserts. The Patagonian Monte Desert on the leeward side of the Andes Mountains in South America is an extreme example of the rain shadow effect.

According to the website http://www.ngdc.noaa.gov, the 95 Arizona Program (NOAA, AMP, and ADWR) measured and simulated orographic induced precipitation over Arizona's watershed. They retrieved information and data by remote sensors and mesoscale/cloud scale and numerically models plotted data. Results of this study indicated that the higher elevations received a significant higher amount of rain and concluded that the steeper the slop the more rain and greater chance of flooding.

I gathered data from worldclimate.com in order to compare the yearly rainfall to the elevation of each region. From this I made a correlation between elevation and the amount of rainfall. The higher the elevation the more rain the region will receive. Although this information gathered is reliable, there are errors that can be made with this project. Orographic precipitation would be better illustrated with more extreme topographic areas. Also a bigger difference in rain totals would be clearer in better suitable regions.

The result of my experiment is that there is a direct correlation between elevation and total rainfall. Therefore my results support my hypothesis. The higher the elevation the more the rainfall fell on that particular region. This research can be applied to everyday life because the study of orographic precipitation can improve the understanding of how the presence of a mountain can modify the climate, and how a climate's response to the mountain can feed back to modify surface feature. It can improve the understanding, analysis, and prediction of precipitation in complex terrains across the world and also the vertical structure of electric fields in continental winter storms. These are just a few of the many studies that are preformed throughout everyday real life research.