Create a main argument, also called a thesis statement. The thesis statement should discuss the major conclusion from looking at, and comparing, the precipitations in your research or experiment. An example thesis statement is: "The rising and falling annual precipitation over the last three years in the greater southwest suggests major shifts in climate and vegetation, which complicates earlier research done on precipitation." In the thesis statement, be sure to include the major implications of the comparison and any pertinent information, such as the timeframe, or type of precipitation, to give your reader an idea of your main argument. This thesis statement will fall near the end of your introductory paragraph in your thesis essay.
Follow the general format for a laboratory report for a scientific investigation when writing about the comparison of precipitation. The first paragraph you will write is an introduction. This paragraph will introduce the reader to the issue of precipitation, previous research done in the field, and why you believe the comparison of precipitation will add to the body of scientific work already done. Include a brief statement about the expected results as well. The thesis statement should conclude the introduction and give the reader your overall conclusion about the work you have done.
Write a section which reflects the methods and materials you used in comparing precipitation. For example, did you use recorded data from the National Weather Service or did you collect data yourself in a controlled environment and a smaller geographic area? This section should clearly describe the steps you took in conducting your research and give a detailed and clear account of your approach to the comparison.
Write a results section, which discusses what information you gleaned from the comparative process. In this section, describe the major conclusions and figures you received from your methods section. For example, if you compared precipitation for two neighboring cities over a three-year period, summarize what these figures tell the reader about the area. Keep from discussing your speculations in this section and keep the writing focused on the results alone.
Write a discussion section to open up a discussion about the implications of the results. In this section, you may begin to posit possible ideas for the importance of changing precipitation patterns, how comparisons may affect the field of climate change, and where you think more work needs to be done. For example, "Research on comparative precipitation for the southern third of Arizona should continue so that we may uncover the shift in climate and vegetation for the entire area." This section is an ideal place to discuss other literature in fields such as climatology, meteorology or vegetation growth and how your work on precipitation fits into previous studies. Use the discussion as your conclusion and restate your main argument concerning your results for comparing precipitation.