Complex sentence: The current population in the mountainous northwestern zone numbers around five million inhabitants and this region has high levels of rainfall (up to 4,000 mm per year) and steep slopes that are susceptible to erosion.
Split into simpler sentences: The current population in the mountainous northwestern zone numbers around five million inhabitants. This region has high levels of rainfall (up to 4,000 mm per year) and steep slopes that are susceptible to erosion.