Interpolation

Discussion

The last El Nino season recorded started in September 2006 and lasted until July 2007. Since then The US has been experienceing a drought until finally now in 2010 we are facing another El Nino. So far however this seems to be a weak El Nino year with the maps showing that rainfall to date this season is almost only at the normal values or even in some areas below normal. However, this may be only because the data for the season ended in March, the entire data set is needed to really determine wether or not this season is an El Nino year or not.

As one can see in the IDW maps the heaviest rainfall seems to have occured in the Eastern central area of LA county. This is consistent in both the Season Total and Season Normal maps. The North Western corner of LA county as seen in the Difference map shows an area that has recieved much less precipitation this season then it normally would.

In the Spline maps where elevation is a negligable factor the dryest areas for this season seem to be the North Eastern area of LA county, this data is also consistent with amount of percipitation expected in a Normal Season. Although most of the maps are fairly similar to each other there are definatly some areas that recieved less precipitation then normal.

The individual rainfall stations store data from specific areas but since we do not have rain gauges every square mile or so we must use interpolation techniques to gather data for the rest of the area.The two types of interpolating techniques I used were Inverse Distance Weighted (IDW) and Spline. The IDW technique works well when a set of points are dense enough to be a representative sample of the whole area. For this lab I judged that we did in fact have a high enough density of rain fall station point to use the IDW interpolation technique. The next technique, Spline, estimates the values using a function that minimizes the curvature of the surface. It predicts “ridges and valleys” in the data set a creates sort of rubber sheet over the data to neutralize these curvatures. It is hard for me to say which technique is better, they each have their strengths and weakness, however it is important to look at the outputs from each of the techniques because they both tell us something unique and valuable.