The patterns and cycles of nature are the dominant context for any climate, and if we want to move from one type of climate (sweltering desert with less than 70 mm rain per year, no carbon in the soil, no organic matter in the soil, evaporation rates exceeding 3000 mm per year, and other foreboding characteristics) to another (productive Savannah yay!) we have to understand both point A and how the major cycles brought you there, and point B–how to work within those cycles to create a different climate.
This post is about understanding point A of where the Arabian Peninsula is (or where it should be) and getting some crucial details of the major cycles determining it climate.
The first cycle we need to know about in the Arabian Gulf is the Inter Tropical Convergence Zone (ITCZ). This is a band of clouds caused by tropical convergences that shifts North and South of the equator (North in the summer and South in the winter from the Northen Hemisphere’s perspective), and due to an unknown number of factors, shifts north or south. In the Indian Ocean, the ITCZ is strongly correlated with summer monsoons. Historically, as the ITCZ has moved North, the monsoons have moved further North, bringing heavy rainfall into Oman and the middle of the gulf. For instance, one particular study that monitored Changing Moisture Sources Over the Last 330,000 Years in Northern Oman found that almost all groundwater recharge in Northern Oman occured at times when the ITCZ shifted north. In other words, when the ITCZ goes north, it pulls rain and monsoons along with it, enough that it is responsible for almost all groundwater in the northern area of Oman. A recent Master’s Thesis from KAUST found that this is actually true for the whole Arabian Peninsula up to a certain latitude–precipitation and the ITCZ follow each other up to a limit of 22 degrees North (which corresponds with Northern Jeddah!)
In short, as the ITCZ shifts North, summertime rainfall in the Arabian Peninsula up to at least 20 degrees latitude North, and potentially as far North as Jeddah.
In that respect, there is good news! The ITCZ has been moving north since the mid 1970s (a recorded .5 degrees North and continuing) which, according to initial studies is increasing cloudiness in Southern Arabia and the Sahel region of Africa, and prompting higher temperatures in Northern Arabia (unfortunateley there are no specifics on what the authors consider Northern Arabia–speculation is it could be as far north as Syria, which could be part of the explanation for one of the longest droughts they’ve had in the Syrian northeast). An increase in cloudiness would typically be associated with an increase in rainfall, but unfortunately, that is not the case in present day Arabia. Despite the ITCZ moving north, rain has actually decreased!
At my work in Al Baydha, which is in the Makkah province of Saudi Arabia, I have had the chance to ask many people about the weather, some of whom are over 80 years old. The old folks in Al Baydha have told me that it used to rain three times a year. These are unlearned people who do not know their own birthdays, but they remember a time when there was a summer rain and two winter rains, and they would feed their animals from trees during the summer by hitting tree trunks with sticks and causing the leaves to fall. In the winter time their animals would eat grass. Other people in Jeddah have informed me that “it has not rained the way it used to in 50 years”. These are anecdotes, but are corroborated by many many witnesses who aren’t just remembering the good old days; they are also struggling with massive shifts in their lives because they can no longer support their animals on their land, due to a lack of rainfall!
How can this be? If the ITCZ has been trending northward since the at least the 1970’s, why is rainfall dropping?
That is the subject of the next post, wherein I will discuss more regional and localized cycles of weather that are fighting (and winning!) against the increased moisture brought on by the ITCZ’s northward trend.