Μελέτη της ξηρασίας στην Νότια Αφρική = Investigating droughts οver South Africa.

Αντώνιος Δημήτριος Τσιγγούδης

Μελέτη της ξηρασίας στην Νότια Αφρική = Investigating droughts οver South Africa.

Αντώνιος Δημήτριος Τσιγγούδης

Περίληψη

Καθώς ο παγκόσμιος πληθυσμός ολοένα και αυξάνεται, ο άνθρωπος και γενικότερα οι κοινωνίες μέσα στις οποίες δραστηριοποιείται ασκούν όλο και μεγαλύτερη πίεση στις ήδη περιορισμένες ποσότητες νερού του πλανήτη, καθώς και σε άλλους φυσικούς πόρους, αυξάνοντας έτσι την ευπάθειά μας στο φαινόμενο της ξηρασίας, τόσο στις ανεπτυγμένες όσο και στις αναπτυσσόμενες χώρες. Επικουρικά, στην όξυνση του προβλήματος αυτού συμβάλλει και η κλιματική αλλαγή στον πλανήτη μας που εξελίσσεται με πρωτόγνωρους ρυθμούς. Γίνεται έτσι αντιληπτό ότι είναι πια επιτακτική η ανάγκη τα έθνη να συνεχίσουν την ανάπτυξη πολιτικών με σκοπό την μείωση των κοινωνικών, οικονομικών και περιβαλλοντικών επιπτώσεων των μελλοντικών γεγονότων ξηρασίας. Οι πολιτικές αυτές θα πρέπει να περικλείουν ένα ευρύ φάσμα τεχνικών διαχείρισης των κινδύνων της ξηρασίας, οι οποίες θα περιλαμβάνουν βελτιωμένα συστήματα παρακολούθησης και έγκαιρης προειδοποίησής της, σχέδια ετοιμότητας και κατάλληλες δράσεις, καθώς και προγράμματα μετριασμού της. Η παρούσα μεταπτυχιακή διπλωματική εργασία πραγματεύεται την ξηρασία στη χώρα της Νότιας Αφρικής. Η Νότια Αφρική λόγω της γεωγραφικής της θέσης και της πολυσχιδούς μορφολογίας της εμφανίζει μεγάλη ποικιλία κλιματικών τύπων και είναι επιρρεπής στην εκδήλωση συχνών ξηρασιών. Ταυτόχρονα, οι μελλοντικές προβολές από τα κλιματικά μοντέλα την τοποθετούν σαν ένα πιθανό hot-spot έντονων ξηρασιών για τον 21 ο αιώνα. Βάσει των παραπάνω, η Νότια Αφρική έχει επιλεγεί από το πρόγραμμα AfriCultuReS σαν μια χώρα μελέτης και εφαρμογής σύγχρονων εργαλείων παρακολούθησης και προειδοποίησης των επεισοδίων ξηρασίας που σκοπό έχουν την καλύτερη διαχείριση της σε επιχειρησιακό επίπεδο, με στόχο τον περιορισμό των επιπτώσεων της. Για την μελέτη αυτών των επεισοδίων στην παρούσα εργασία επιλέχτηκαν τρεις δείκτες ξηρασίας ποσοτικής εκτίμησης με δεδομένα από την 1/1/2017 έως την 31/12/2020. Οι δείκτες αυτοί είναι: ο Τυποποιημένος Δείκτης Βροχόπτωσης και Εξατμισοδιαπνοής - SPEI, σε τρεις χρονικές κλίμακες του ενός, των τριών και των δώδεκα μηνών, ο Δείκτης Κατάστασης της Εδαφικής Υγρασίας - SWCI και ο Δείκτης Κατάστασης της Βλάστησης - VCI. ανάλυση των δεικτών επιβεβαίωσε τρία σημαντικά επεισόδια ξηρασίας, με μεγάλη διάρκεια, έντονα χαρακτηριστικά και μεγάλη χωρική κατανομή. Τα επεισόδια αυτά αποτέλεσαν τρεις μελέτες περίπτωσης (case study), όπου για την επιβεβαίωσή τους εξετάστηκαν οι βιβλιογραφικές αναφορές και οι επίγειες παρατηρήσεις από τους μετεωρολογικούς σταθμούς της Εθνικής Μετεωρολογικής Υπηρεσίας της Νοτίου Αφρικής. Διαπιστώθηκε από την ανάλυση ότι οι δείκτες παρουσιάζουν παρόμοια συμπεριφορά με ταύτιση των περιόδων ξηρασίας ως προς την χρονική και χωρική τους κατανομή, και μεγάλη συμφωνία με τις επικρατούσες συνθήκες στην Νότια Αφρική τις περιόδους αυτές. Καταλήγουμε έτσι στο συμπέρασμα ότι πρόκειται για εύχρηστους και αξιόπιστους δείκτες ποσοτικής εκτίμησης των διαφόρων τύπων της ξηρασίας (μετεωρολογικής, γεωργικής, υδρολογικής).
Λέξεις κλειδιά: Ξηρασία, Νότια Αφρική, Δείκτες ξηρασίας, SPEI, SWCI, VCI, AfriCultuReS

As the world population grows, humans and the societies in which they are active are increasingly putting pressure on the already limited amounts of the planet’s water supplies, as well as on other natural resources, thus increasing our vulnerability to drought, both in developed and developing countries. In addition, climate change, which is evolving at an unprecedented rate on the planet, also contributes to the exacerbation of this problem. It is thus understood that there is an urgent need for nations to continue to develop policies aimed at reducing the social, economic, and environmental impact of future drought events. These policies should include a wide range of drought risk management techniques, which will include improved monitoring and early warning systems, preparedness plans and appropriate actions, as well as mitigation programs. The present master thesis focuses on the drought in the country of South Africa. Due to its geographical location and diverse morphology, South Africa has a wide variety of climatic types and is prone to frequent droughts. At the same time, climate models’ future projections describe it as a possible hot-spot of intense droughts for the 21 st century. Based on the above, South Africa has been selected by the AfriCultuReS program as a country for the study and implementation of modern tools for monitoring and warning of drought events that aim to better manage them at operational level, in order to limit their impact. In order to study these drought events, three quantitative drought indices were selected and utilized with data from 1/1/2017 to 31/12/2020. These indices are the Standardized Precipitation Evapotranspiration Index - SPEI, in three-time scales of one, three and twelve months, the Soil Water Condition Index - SWCI and the Vegetation Condition Index - VCI. The analysis of the indices revealed three important drought events, with long duration, strong characteristics and large spatial distribution. These events were three case studies, and for their confirmation the bibliographic reports and the earth observations from the meteorological stations of the National Meteorological Service of South Africa were examined. Combining the results of this analysis, the indices present a similar behavior with the identification of drought periods in terms of their temporal and spatial distribution, and a great agreement with the predominant conditions in South Africa during these periods. We thus conclude that these are easy-to-use and reliable indices for quantitative estimation of the different types of droughts (meteorological, agricultural, hydrological).
Keywords: Drought, South Africa, Drought Indices, SPEI, SWCI, VCI, AfriCultuReS

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