# Charts - Rain charts

## Introduction

The Rain charts submodule consists of five charts:

- Daily Rain - Plotting the rainfall for every day in the dayfile;
- Monthly Rain - Plotting the monthly rainfall for every year in the dayfile
- Yearly Rain statistics - Plotting the average, range and standard deviation for for the rainfall in every year
- Yearly Rain statistics per month = plotting the average, range and standard deviation for for the rainfall in each month in every year
- Rain versus EvapoTranspiration (EVT)

Below you will find an example image of each chart and an explanation of the origin of the numbers

For the calculations the standard C# LINQ-functions Min, Max and Avg are used. For the standard deviation this LINQ-extension is used with a modification for a minimum number of observations required of 2, if less the StdDev returns 0 (zero).

## Daily Rain

The chart is a timeseries of rainfall with data coming from the Dayfile. Every day it rained it is plotted in the chart as column. The cumulative value of the rain starts january 1 at zero and augments with every amount measured until 31 december after which it resets to zero. Also visible is a moving average with a configurable period (default is 180 days).

If the value of the inifile parameter *UseNormalRainReference* is *Normal* the user sees a red dotted horizontal line at the Y-axis value of the Normal total rainfall per year. When *UseNormalRainReference* is *StationAverage* the user sees a green dotted line ate the value of the calculated average total rainfall for the station. And obviously when the parameter value is both, the user sees both lines.

There are three Y-axis: one on the left, the main Y-axis, showing the actual rainfall amount. On the right we see the Y-axis with value of the moving average and the Y-axis with the value of the accumulated rainfall value.

The rangeselector gives the user the option to view a selected period with fixed buttons (left) or by specific dates (right).

## Monthly Rain

The chart shows the monthly values of total rain that month for each year. The years have a different colour according to the colour scheme. The number of series directly visible is governed by the parameter MaxNrOfSeriesVisibleInGraphs.

If the value of the inifile parameter UseNormalRainReference is *Normal* the user sees a black line representing the normal average values of total rainfall. When UseNormalRainReference is *StationAverage* the user sees a grey line representing the station average values of total rainfall. And obviously when the parameter value is *Both*, the user sees both lines. In addition to the Station Average Value line, the estimator **s** for the standard deviation belonging to that line, is always shown as a grey surface with the width of **s** for a specific month.

## Yearly Rain statistics

For each year the charts shows the average of the daily rainfall, the range of the daily rain fall and the estimator **s** for the standard deviation belonging to that average. The colours of this chart are hardcoded and cannot be changed. Moving the mouse around provides the specific values in the tooltips.

NOTE: the Y-axis scale is logarithmic. This type of scaling has provided for possible negative values to accommodate proper charting even if not mathematical correct.

## Yearly Rain statistics per Month

This chart is similar to the previous one, only now the the user can select a specific month through a row of buttons on top of the chart.

## Rain versus EvapoTranspiration (EVT)

The cumulative rain is plotted versus the cumulative evapotranspiration. The latter coming either from the device (Davis) or calculated by CMX. The plot is implemented as a coloured area plot showing a surplus of rain in green and a rain deficit as red. Best is to show some years from the start of the rain season (use the date selector).

This chart is an effort to graphically display droughts. It must be understood that EVT is a very complex meteorological aggregate in that it is highly dependent on the interaction between soil, vegetation and meteorology. CMX uses only one equation for all situations on earth. That equation seems to be fitted to the moderate climate. As such it bypasses plant strategies to battle drought and low humidity situations such as the stomata closure and deep rooting. The chart as such must be used with some caution.

It is advised to always use the CMX calculation as that would result in comparable charts. CMX uses the FAO Penman-Monteith equation with reference to the implementation of Weewx.

The user is advised not to take the EvapoTranspiration figures as absolute but, for a good understanding of the complexity of EvapoTranspiration, to study the relevant chapter *FAO Crop evapotranspiration - Guidelines for computing crop water requirements - FAO Irrigation and drainage paper 56*.