The variable called ME measures the intensity of malaria transmission based on the type of mosquitos abundant in each area. Here's my own summary of how this variable is constructed (see Kiszewski et al 2004 for detail).
1. Obtain the human-biting intensity (a) and the daily survival rate (p) for each type of mosquitos.
2. Obtain the duration of extrinsic incubation period for parasites in each month from monthly temperature.
3. For each location-month, identify the type of mosquitos.
4. Calculate the transmission intensity for each location-month by the formula in Kiszewski et al 2004 and sum them over a year for each location.