Monthly Precipitation over Northern Middle Atlas, Eastern Morocco: Homogenization and Trends

Abstract

The lack of a complete and reliable data series often represents the main difficulty in carrying out climate studies. Diverse causes, such as human and instrumental errors, false and incomplete records, and the use of obsolete equipment in some meteorological stations, give rise to inhomogeneities that do not represent climatic reality. This work in the northern part of the Moroccan Middle Atlas used 22 meteorological stations with sometimes-incomplete monthly precipitation data from 1970 to 2019. The homogenization and estimation of the missing data were carried out with the R software package Climatol version 3.1.1. The trends in the series were quantified by the Mann–Kendall nonparametric test. The results obtained show a low root mean square error (RMSE), between the original and homogenized data, of between 0.5 and 38.7 mm per month, with an average of 8.5 mm. Rainfall trends for the months of December through June are generally downward. These negative trends are significantly stronger in the southern and eastern parts of the study area, especially during the month of April (the wettest month). On the other hand, July shows positive trends, with 71% of stations having an increasing precipitation tendency, although only five (or 1/3) of these are statistically significant. From August to November, generally positive trends were also observed. For these months, the percentage of series with a positive and significant trend varied between 55 and 77%.

Statistical Analysis for the Detection of Change Points and the Evaluation of Monthly Mean Temperature Trends of the Moulouya Basin (Morocco)

“…Te expansive and diverse topography of the Moulouya watershed gives rise to a wide range of climatic conditions. Tese conditions span from a Mediterranean climate in the lower Moulouya to a relatively cooler continental climate in the upper Moulouya and even to an arid, Saharan-like climate in the Guercif Basin and the mountainous regions of the middle Moulouya [56][57][58]. Annual rainfall levels are relatively low and erratic, with cumulative annual precipitation ranging from less than 100 mm to slightly over 600 mm, depending on the specifc region [59].…”

“…To this end, in order to test data quality, we opted for the Climatol tool (version 3.1.1, https:// www.climatol.eu/, downloaded on December 15, 2022). Tis tool is recommended by several climatologists [56,[60][61][62]. Te stations where data were collected are summarized in the table as follows.…”