Blue and green water: why they affect us all

Address­ing the water cri­sis is imper­a­tive for glob­al cli­mate adap­ta­tion. Cur­rent water poli­cies focus pri­mar­i­ly on vis­i­ble, or « blue, » water sources, often over­look­ing the crit­i­cal role of « green » water, stored in soil and veg­e­ta­tion, con­sti­tut­ing about 60% of glob­al land pre­cip­i­ta­tion. Recog­nis­ing water as a Glob­al Com­mon Good (GCG) is essen­tial for achiev­ing cli­mate goals and Sus­tain­able Devel­op­ment Goals (SDGs).

At COP29, nego­ti­a­tions aim to achieve agree­ments to respond to the water cri­sis ade­quate­ly; how­ev­er, to do so, a prop­er under­stand­ing of the under­ly­ing hydro­log­i­cal cycle is nec­es­sary. The water, or hydro­log­i­cal cycle, is under­stood as “[…] a com­plex sys­tem with dif­fer­ent stores inter­act­ing with vary­ing strengths and over a wide range of scales with oth­er com­po­nents of the Earth sys­tem such as atmos­phere, bios­phere, and lithos­phere¹”  and it is dri­ven by solar radi­a­tion and grav­i­ty, with water chang­ing into dif­fer­ent states (liq­uid, gas, sol­id) and mov­ing between the atmos­phere, ocean and land. It evap­o­rates and tran­spires from land and water bod­ies, then gets trans­port­ed, con­densed, and ulti­mate­ly pre­cip­i­tates back onto the Earth­’s surface.

World­wide, we are cur­rent­ly push­ing the hydro­log­i­cal cycle out of bal­ance. Through human-induced cli­mate change, defor­esta­tion, and loss of bio­di­ver­si­ty, we are chang­ing pre­cip­i­ta­tion pat­terns. As tem­per­a­ture ris­es, the cycle inten­si­fies and evap­o­rates more water lead­ing to more extreme weath­er events, like extreme rain­fall, hur­ri­canes and coastal floods². 

Cur­rent water poli­cies pri­mar­i­ly focus on vis­i­ble water sources, such as rivers and oceans (blue water), while fre­quent­ly neglect­ing the impor­tance of green water. Nonethe­less, sci­en­tif­ic evi­dence shows that around 60% of the pre­cip­i­ta­tion that falls on land ends up stored as green water ‑fur­ther indi­cat­ing that green water is the largest con­trib­u­tor to fresh­wa­ter glob­al­ly³. The impor­tance of green water is fur­ther addressed by Friedling­stein et al⁴., who high­light that green water in soils is of neces­si­ty for land-based ecosys­tems, which can absorb 25–30% of car­bon diox­ide emit­ted from fos­sil fuels.

Fig­ure 1 rep­re­sents the glob­al net­work of ter­res­tri­al mois­ture flows between dif­fer­ent regions, show­ing how inter­con­nect­ed our world is via wind rivers. The arrows rep­re­sent the direc­tion of mois­ture flow, through two process­es: evap­o­tran­spi­ra­tion, the process where water is trans­ferred from land to the atmos­phere by evap­o­ra­tion and tran­spi­ra­tion (from plants), and pre­cip­i­ta­tion, mois­ture that returns to the land as rain­fall. There are also points pre­sent­ing the geo­graph­i­cal cen­tre of each coun­try to demon­strate that water evap­o­tran­spires and pre­cip­i­tates from every coun­try towards the rest of the world. Hence, the net­work show­cas­es that coun­tries are high­ly inter­con­nect­ed when it comes to mois­ture flows. This is sci­en­tif­ic evi­dence that water evap­o­rat­ed from one region with­in a coun­try can sig­nif­i­cant­ly impact rain­fall in dis­tant regions; coun­tries are even more inter­con­nect­ed in terms of the hydro­log­i­cal cycle than pre­vi­ous­ly thought.

Sim­i­lar to riv­er basins and aquifers, atmos­pher­ic mois­ture car­ries water from one coun­try to anoth­er, across oceans and con­ti­nents⁵, mean­ing that wind rivers can be tracked to demon­strate how eco­nom­ic activ­i­ties tak­ing place in one region or coun­try can impact oth­ers down­wind.

For exam­ple, water evap­o­ra­tion in West Africa is trans­port­ed down­wind to the Ama­zon Rain­for­est (most­ly Brazil), where it arrives in the form of rain­fall. Now, in the last decade, Brazil has pro­mot­ed poli­cies of heavy deple­tion of the Ama­zon Rainforest’s resources, which are lead­ing to a loss of green water avail­abil­i­ty as the land’s capac­i­ty to store and use green water dis­ap­pears. Hence, there is less green water that can be evap­o­rat­ed in the Ama­zon Rain­for­est to be trans­port­ed fur­ther down­wind to neigh­bour­ing coun­tries. This is the case in coun­tries such as Colom­bia, which rely heav­i­ly on rain­fall water for con­sump­tion and ener­gy pro­duc­tion since resource deple­tion in Brazil has led to a low­er water yield⁶. 

Glob­al inter­con­nec­tion in the water cycle is a fact, and it means we must start address­ing the water cri­sis holis­ti­cal­ly where both green and blue water are at the fore­front of glob­al-scale poli­cies and pacts.

If water is part of this com­plex sys­tem called the hydro­log­i­cal ‑or water- cycle, gov­ern­ing it requires a shift in per­cep­tion of the way it is con­ceived. Water must be increas­ing­ly under­stood as a Glob­al Com­mon Good (GCG). But what exact­ly does this con­cept entail?

First, recog­nis­ing water as a GCC is acknowl­edg­ing that com­mu­ni­ties, coun­tries, and regions are inter­con­nect­ed, not only through vis­i­ble water resources (blue water, such as rivers and lakes) but also through atmos­pher­ic mois­ture flows and green water (water stored in soil and veg­e­ta­tion). Sec­ond, this shift posi­tions water high up in the inter­na­tion­al agen­da since it under­stands that the Anthropocene’s impact on the hydro­log­i­cal cycle is intri­cate­ly con­nect­ed with the pres­sure it puts on oth­er alarm­ing process­es such as cli­mate change and bio­di­ver­si­ty loss; for instance, a sta­ble sup­ply of green water is cru­cial for absorb­ing car­bon diox­ide and sup­port­ing ecosystems.

More­over, this con­cept avoids treat­ing water in a siloed man­ner when it comes to SDGs. The water cri­sis is not only an issue to solve via SDG 6 – which most­ly deals with WASH (Water, san­i­ta­tion and hygiene). Water is fun­da­men­tal to achiev­ing vir­tu­al­ly all the SDGs since a desta­bilised hydro­log­i­cal cycle threat­ens food secu­ri­ty, eco­nom­ic sta­bil­i­ty, pub­lic health, and social equi­ty, which are cor­ner­stones of sus­tain­able devel­op­ment⁷.

At COP29 in Baku, nego­tia­tors had a unique oppor­tu­ni­ty to pro­mote an inte­grat­ed approach to solve the water cri­sis and lay foun­da­tion­al steps towards a uni­fied Glob­al Water Pact by agree­ing to the Baku Dec­la­ra­tion on Water.

Dur­ing Novem­ber 19^th (the day ded­i­cat­ed to food, agri­cul­ture, and water) key inputs were dis­cussed for the Dec­la­ra­tion. A cru­cial first out­come was the com­mit­ment to “[…] pro­mote dia­logue and part­ner­ships [by] strength­en­ing COP-to-COP syn­er­gies [and] sup­port­ing the devel­op­ment of col­lab­o­ra­tive and aligned cli­mate action pol­i­cy⁸”. This com­mit­ment is a mile­stone in estab­lish­ing a Glob­al Water Pact as it places the hydro­log­i­cal cycle as a whole at the heart of the Rio Trio – UNFCCC, UNCBD and UNCCD. After all, we know water secu­ri­ty, con­ser­va­tion, and sus­tain­able man­age­ment must be treat­ed inte­gral­ly to achieve cli­mate goals⁹.

The Dec­la­ra­tion on Water, also framed water as a foun­da­tion­al ele­ment in cli­mate action, as it asks coun­tries to com­mit to “[…] effec­tive­ly inte­grate water con­sid­er­a­tions in the design of cli­mate poli­cies, includ­ing nation­al adap­ta­tion plans (NAPs) or strate­gies, nation­al­ly deter­mined con­tri­bu­tions (NDCs), and asso­ci­at­ed imple­men­ta­tion plans, as well as nation­al bio­di­ver­si­ty strate­gies and action plans (NBSAPs) […]”. Now, the dec­la­ra­tion was not explic­it on the need to set clear glob­al tar­gets relat­ed to water con­ser­va­tion in its green and blue forms, lim­it­ing the sup­port for inter­na­tion­al progress quan­tifi­ca­tion poli­cies, a cru­cial aspect for a well-designed Glob­al Water Pact¹⁰.

Finan­cial com­mit­ments were lack­ing on the Dec­la­ra­tion on Water. For a Glob­al Water Pact to become a real­i­ty, both, coun­tries and finan­cial insti­tu­tions need to pledge invest­ments in sus­tain­able water infra­struc­ture, inno­v­a­tive tech­nolo­gies, and con­ser­va­tion efforts, which the Dec­la­ra­tion does not back. Addi­tion­al­ly, the need for trans­paren­cy and account­abil­i­ty around water and its resource-relat­ed uses (such as defor­esta­tion and ener­gy pro­duc­tion) was not explic­it­ly stat­ed. Hence, back­ing pro­pos­als such as the stan­dard­i­s­a­tion of data shar­ing process, green and blue water foot­print dis­clo­sures, and sus­tain­able cor­po­rate water prac­tices, which facil­i­tate busi­ness­es’ account­abil­i­ty in terms of impact to the hydro­log­i­cal cycle¹¹ becomes harder.

A big win in terms of social inclu­sion was achieved on the Dec­la­ra­tion on Water. The fifty sig­na­to­ry coun­tries agreed to include the need to incor­po­rate per­spec­tives from often mar­gin­alised com­mu­ni­ties such as indige­nous peo­ples, migrants and youth. A Glob­al Water Pact will inher­ent­ly need these voic­es to shape suc­cess­ful poli­cies that pro­tect local water resources in their blue and green forms and respect tra­di­tion­al knowl­edge since indige­nous com­mu­ni­ties are stew­ards of nat­ur­al resources, and young peo­ple are heirs of the con­se­quences of today’s water poli­cies¹².

As sci­en­tif­ic evi­dence proves that the hydro­log­i­cal cycle con­nects coun­tries and regions far more deeply than pre­vi­ous­ly thought, a Glob­al Water Pact seems to be the most ambi­tious, yet cru­cial way to address the water cri­sis. COP29 had a key oppor­tu­ni­ty: to ini­ti­ate a for­mal roadmap toward a Glob­al Water Pact by out­lin­ing the role of water in cli­mate action.

By no means is this dec­la­ra­tion per­fect: it does not pro­mote a frame­work for water and cli­mate finance, and it miss­es the chance of back­ing set goals for cli­mate action. Yet, the Dec­la­ra­tion also sup­ports the need for COP-to-COP col­lab­o­ra­tion, pro­motes the inte­gra­tion of water – implic­it­ly both blue and green – on nation­al devel­op­ment plans, and calls for the voice of indige­nous peo­ples and youth to be at the fore­front of the debate. Over­all, the Dec­la­ra­tion on Water for Cli­mate action signed at Baku dur­ing COP29 increas­es the momen­tum that water has gained in the past few years at the inter­na­tion­al scale and as UNCCD (the key COP for water action) approach­es, the inter­na­tion­al com­mu­ni­ty should fol­low close­ly the steps those coun­tries will take to keep increas­ing water vis­i­bil­i­ty on the inter­na­tion­al agenda.